diff --git a/web/src/main/kotlin/com/wbrawner/twigs/web/WebRoutes.kt b/web/src/main/kotlin/com/wbrawner/twigs/web/WebRoutes.kt
index bcb417c..d957e1a 100644
--- a/web/src/main/kotlin/com/wbrawner/twigs/web/WebRoutes.kt
+++ b/web/src/main/kotlin/com/wbrawner/twigs/web/WebRoutes.kt
@@ -7,6 +7,7 @@ import com.wbrawner.twigs.service.category.CategoryService
 import com.wbrawner.twigs.service.transaction.TransactionService
 import com.wbrawner.twigs.service.user.UserService
 import com.wbrawner.twigs.web.budget.budgetWebRoutes
+import com.wbrawner.twigs.web.category.categoryWebRoutes
 import com.wbrawner.twigs.web.user.userWebRoutes
 import io.ktor.server.application.*
 import io.ktor.server.http.content.*
@@ -43,5 +44,6 @@ fun Application.webRoutes(
         }
     }
     budgetWebRoutes(budgetService, categoryService, transactionService, userService)
+    categoryWebRoutes(budgetService, categoryService, transactionService, userService)
     userWebRoutes(userService)
 }
\ No newline at end of file
diff --git a/web/src/main/kotlin/com/wbrawner/twigs/web/budget/BudgetPages.kt b/web/src/main/kotlin/com/wbrawner/twigs/web/budget/BudgetPages.kt
index 70165e1..86c44ae 100644
--- a/web/src/main/kotlin/com/wbrawner/twigs/web/budget/BudgetPages.kt
+++ b/web/src/main/kotlin/com/wbrawner/twigs/web/budget/BudgetPages.kt
@@ -1,9 +1,9 @@
 package com.wbrawner.twigs.web.budget
 
 import com.wbrawner.twigs.service.budget.BudgetResponse
-import com.wbrawner.twigs.service.category.CategoryResponse
 import com.wbrawner.twigs.service.user.UserResponse
 import com.wbrawner.twigs.web.AuthenticatedPage
+import com.wbrawner.twigs.web.category.CategoryWithBalanceResponse
 
 data class BudgetListPage(
     val budgets: List<BudgetListItem>,
@@ -26,14 +26,6 @@ data class BudgetDetailsPage(
     override val error: String? = null
 ) : AuthenticatedPage {
     override val title: String = "Budgets"
-
-    data class CategoryWithBalanceResponse(
-        val category: CategoryResponse,
-        val amountLabel: String,
-        val balance: Long,
-        val balanceLabel: String,
-        val remainingAmountLabel: String,
-    )
 }
 
 data class BudgetFormPage(
diff --git a/web/src/main/kotlin/com/wbrawner/twigs/web/budget/BudgetWebRoutes.kt b/web/src/main/kotlin/com/wbrawner/twigs/web/budget/BudgetWebRoutes.kt
index 3ccbd35..244c34e 100644
--- a/web/src/main/kotlin/com/wbrawner/twigs/web/budget/BudgetWebRoutes.kt
+++ b/web/src/main/kotlin/com/wbrawner/twigs/web/budget/BudgetWebRoutes.kt
@@ -12,6 +12,7 @@ import com.wbrawner.twigs.service.transaction.TransactionService
 import com.wbrawner.twigs.service.user.UserService
 import com.wbrawner.twigs.toInstantOrNull
 import com.wbrawner.twigs.web.NotFoundPage
+import com.wbrawner.twigs.web.category.CategoryWithBalanceResponse
 import com.wbrawner.twigs.web.user.TWIGS_SESSION_COOKIE
 import io.ktor.http.*
 import io.ktor.server.application.*
@@ -103,7 +104,7 @@ fun Application.budgetWebRoutes(
                             .map { category ->
                                 val categoryBalance =
                                     abs(transactionService.sum(categoryId = category.id, userId = user.id))
-                                BudgetDetailsPage.CategoryWithBalanceResponse(
+                                CategoryWithBalanceResponse(
                                     category = category,
                                     amountLabel = category.amount.toCurrencyString(numberFormat),
                                     balance = categoryBalance,
@@ -225,6 +226,6 @@ private fun <T> MutableCollection<T>.extractIf(predicate: (T) -> Boolean): List<
     return extracted
 }
 
-private fun Long.toCurrencyString(formatter: NumberFormat): String = formatter.format(
+fun Long.toCurrencyString(formatter: NumberFormat): String = formatter.format(
     this.toBigDecimal().divide(BigDecimal(100), 2, RoundingMode.HALF_UP)
 )
\ No newline at end of file
diff --git a/web/src/main/kotlin/com/wbrawner/twigs/web/category/CategoryPages.kt b/web/src/main/kotlin/com/wbrawner/twigs/web/category/CategoryPages.kt
new file mode 100644
index 0000000..d1759cb
--- /dev/null
+++ b/web/src/main/kotlin/com/wbrawner/twigs/web/category/CategoryPages.kt
@@ -0,0 +1,58 @@
+package com.wbrawner.twigs.web.category
+
+import com.wbrawner.twigs.service.budget.BudgetResponse
+import com.wbrawner.twigs.service.category.CategoryResponse
+import com.wbrawner.twigs.service.transaction.TransactionResponse
+import com.wbrawner.twigs.service.user.UserResponse
+import com.wbrawner.twigs.web.AuthenticatedPage
+import com.wbrawner.twigs.web.budget.toCurrencyString
+import java.text.NumberFormat
+
+data class CategoryDetailsPage(
+    val category: CategoryWithBalanceResponse,
+    val budgets: List<BudgetResponse>,
+    val transactionCount: String,
+    val transactions: List<Map.Entry<String, List<TransactionListItem>>>,
+    override val user: UserResponse,
+    override val error: String? = null
+) : AuthenticatedPage {
+    override val title: String = category.category.title
+}
+
+data class TransactionListItem(
+    val id: String,
+    val title: String,
+    val description: String,
+    val budgetId: String,
+    val expenseClass: String,
+    val amountLabel: String
+)
+
+fun TransactionResponse.toListItem(numberFormat: NumberFormat) = TransactionListItem(
+    id,
+    title.orEmpty(),
+    description.orEmpty(),
+    budgetId,
+    if (expense != false) "expense" else "income",
+    (amount ?: 0L).toCurrencyString(numberFormat)
+)
+
+data class CategoryFormPage(
+    val category: CategoryResponse,
+    override val user: UserResponse,
+    override val error: String? = null
+) : AuthenticatedPage {
+    override val title: String = if (category.id.isBlank()) {
+        "New Category"
+    } else {
+        "Edit Category"
+    }
+}
+
+data class CategoryWithBalanceResponse(
+    val category: CategoryResponse,
+    val amountLabel: String,
+    val balance: Long,
+    val balanceLabel: String,
+    val remainingAmountLabel: String,
+)
\ No newline at end of file
diff --git a/web/src/main/kotlin/com/wbrawner/twigs/web/category/CategoryWebRoutes.kt b/web/src/main/kotlin/com/wbrawner/twigs/web/category/CategoryWebRoutes.kt
new file mode 100644
index 0000000..1794aa1
--- /dev/null
+++ b/web/src/main/kotlin/com/wbrawner/twigs/web/category/CategoryWebRoutes.kt
@@ -0,0 +1,180 @@
+package com.wbrawner.twigs.web.category
+
+import com.wbrawner.twigs.endOfMonth
+import com.wbrawner.twigs.firstOfMonth
+import com.wbrawner.twigs.service.HttpException
+import com.wbrawner.twigs.service.budget.BudgetService
+import com.wbrawner.twigs.service.category.CategoryRequest
+import com.wbrawner.twigs.service.category.CategoryResponse
+import com.wbrawner.twigs.service.category.CategoryService
+import com.wbrawner.twigs.service.requireSession
+import com.wbrawner.twigs.service.transaction.TransactionService
+import com.wbrawner.twigs.service.user.UserService
+import com.wbrawner.twigs.toInstant
+import com.wbrawner.twigs.toInstantOrNull
+import com.wbrawner.twigs.web.NotFoundPage
+import com.wbrawner.twigs.web.budget.toCurrencyString
+import com.wbrawner.twigs.web.user.TWIGS_SESSION_COOKIE
+import io.ktor.http.*
+import io.ktor.server.application.*
+import io.ktor.server.auth.*
+import io.ktor.server.mustache.*
+import io.ktor.server.request.*
+import io.ktor.server.response.*
+import io.ktor.server.routing.*
+import io.ktor.server.util.*
+import io.ktor.util.date.*
+import java.text.DateFormat
+import java.text.NumberFormat
+import java.util.*
+import kotlin.math.abs
+
+fun Application.categoryWebRoutes(
+    budgetService: BudgetService,
+    categoryService: CategoryService,
+    transactionService: TransactionService,
+    userService: UserService
+) {
+    routing {
+        authenticate(TWIGS_SESSION_COOKIE) {
+            route("/budgets/{budgetId}/categories") {
+                get {
+                    val budgetId = call.parameters.getOrFail("budgetId")
+                    call.respondRedirect("/budgets/$budgetId")
+                }
+
+                route("/new") {
+                    get {
+                        val user = userService.user(requireSession().userId)
+                        val budgetId = call.parameters.getOrFail("budgetId")
+                        call.respond(
+                            MustacheContent(
+                                "category-form.mustache",
+                                CategoryFormPage(
+                                    CategoryResponse(
+                                        id = "",
+                                        title = "",
+                                        description = "",
+                                        amount = 0,
+                                        budgetId = budgetId,
+                                        expense = true,
+                                        archived = false,
+                                    ),
+                                    user
+                                )
+                            )
+                        )
+                    }
+
+                    post {
+                        val user = userService.user(requireSession().userId)
+                        val budgetId = call.parameters.getOrFail("budgetId")
+                        try {
+                            val request = call.receiveParameters().toCategoryRequest()
+                            val category = categoryService.save(request, user.id)
+                            call.respondRedirect("/budgets/${category.budgetId}/categories/${category.id}")
+                        } catch (e: HttpException) {
+                            call.respond(
+                                status = e.statusCode,
+                                MustacheContent(
+                                    "category-form.mustache",
+                                    CategoryFormPage(
+                                        CategoryResponse(
+                                            id = "",
+                                            title = call.parameters["title"].orEmpty(),
+                                            description = call.parameters["description"].orEmpty(),
+                                            amount = call.parameters["amount"]?.toLongOrNull() ?: 0L,
+                                            expense = call.parameters["expense"]?.toBoolean() ?: false,
+                                            archived = call.parameters["archived"]?.toBoolean() ?: false,
+                                            budgetId = budgetId
+                                        ),
+                                        user,
+                                        e.message
+                                    )
+                                )
+                            )
+                        }
+                    }
+                }
+
+                route("/{id}") {
+                    get {
+                        val user = userService.user(requireSession().userId)
+                        val categoryId = call.parameters.getOrFail("id")
+                        // TODO: Allow user-configurable locale
+                        val numberFormat = NumberFormat.getCurrencyInstance(Locale.US)
+                        try {
+                            val category = categoryService.category(categoryId = categoryId, userId = user.id)
+                            val categoryBalance =
+                                abs(transactionService.sum(categoryId = category.id, userId = user.id))
+                            val categoryWithBalance = CategoryWithBalanceResponse(
+                                category = category,
+                                amountLabel = category.amount.toCurrencyString(numberFormat),
+                                balance = categoryBalance,
+                                balanceLabel = categoryBalance.toCurrencyString(numberFormat),
+                                remainingAmountLabel = (category.amount - categoryBalance).toCurrencyString(numberFormat)
+                            )
+                            val transactions = transactionService.transactions(
+                                budgetIds = listOf(category.budgetId),
+                                categoryIds = listOf(category.id),
+                                from = call.parameters["from"]?.toInstantOrNull() ?: firstOfMonth,
+                                to = call.parameters["to"]?.toInstantOrNull() ?: endOfMonth,
+                                userId = user.id
+                            )
+                            val transactionCount = NumberFormat.getNumberInstance(Locale.US)
+                                .format(transactions.size)
+                            val dateFormat = DateFormat.getDateInstance(DateFormat.SHORT, Locale.US)
+                            val transactionsByDate = transactions.groupBy {
+                                dateFormat.format(it.date.toInstant().toGMTDate().toJvmDate())
+                            }
+                                .mapValues { (_, transactions) -> transactions.map { it.toListItem(numberFormat) } }
+                                .entries
+                                .sortedBy { it.key }
+                            call.respond(
+                                MustacheContent(
+                                    "category-details.mustache", CategoryDetailsPage(
+                                        category = categoryWithBalance,
+                                        transactions = transactionsByDate,
+                                        transactionCount = transactionCount,
+                                        budgets = budgetService.budgetsForUser(user.id),
+                                        user = user
+                                    )
+                                )
+                            )
+                        } catch (e: HttpException) {
+                            call.respond(
+                                status = e.statusCode,
+                                MustacheContent("404.mustache", NotFoundPage)
+                            )
+                        }
+                    }
+
+                    route("/edit") {
+                        get {
+                            val user = userService.user(requireSession().userId)
+                            val category = categoryService.category(
+                                categoryId = call.parameters.getOrFail("id"),
+                                userId = user.id
+                            )
+                            call.respond(
+                                MustacheContent(
+                                    "category-form.mustache",
+                                    CategoryFormPage(category, user)
+                                )
+                            )
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+private fun Parameters.toCategoryRequest() = CategoryRequest(
+    title = get("title"),
+    description = get("description"),
+    amount = get("amount")?.toLongOrNull(),
+    expense = get("expense")?.toBoolean(),
+    archived = get("archived")?.toBoolean(),
+    budgetId = get("budgetId"),
+)
\ No newline at end of file
diff --git a/web/src/main/resources/static/style.css b/web/src/main/resources/static/style.css
index 8ce3f75..3b31a96 100644
--- a/web/src/main/resources/static/style.css
+++ b/web/src/main/resources/static/style.css
@@ -60,6 +60,8 @@ main {
     height: 100%;
     overflow-y: auto;
     flex-grow: 1;
+    padding: 1rem;
+    box-sizing: border-box;
 }
 
 .sidebar {
diff --git a/web/src/main/resources/templates/category-details.mustache b/web/src/main/resources/templates/category-details.mustache
new file mode 100644
index 0000000..1766199
--- /dev/null
+++ b/web/src/main/resources/templates/category-details.mustache
@@ -0,0 +1,36 @@
+{{> partials/head }}
+<div id="app">
+    {{>partials/sidebar}}
+    <main>
+        <div class="column">
+            <h1>{{category.category.title}}</h1>
+            <p>{{category.category.description}}</p>
+            <div class="row">
+                <div class="stacked-label">
+                    <p class="body-small">Budgeted</p>
+                    <p class="body-large">{{category.amountLabel}}</p>
+                </div>
+                <div class="stacked-label">
+                    <p class="body-small">Actual</p>
+                    <p class="body-large">{{category.balanceLabel}}</p>
+                </div>
+                <div class="stacked-label">
+                    <p class="body-small">Remaining</p>
+                    <p class="body-large">{{category.remainingAmountLabel}}</p>
+                </div>
+            </div>
+            <progress value="{{category.balance}}"
+                      max="{{category.category.amount}}">{{category.balanceLabel}}</progress>
+        </div>
+        <!-- TODO: Add a search bar to filter transactions by name/description -->
+        <div class="card">
+            <h3>Transactions</h3>
+            <ul>
+                {{#transactions}}
+                    {{>partials/transaction-list}}
+                {{/transactions}}
+            </ul>
+        </div>
+    </main>
+</div>
+{{>partials/foot}}
\ No newline at end of file
diff --git a/web/src/main/resources/templates/partials/category-list.mustache b/web/src/main/resources/templates/partials/category-list.mustache
index 0af4144..a9de2c9 100644
--- a/web/src/main/resources/templates/partials/category-list.mustache
+++ b/web/src/main/resources/templates/partials/category-list.mustache
@@ -1,5 +1,5 @@
 <li class="list-item">
-    <a href="/categories/{{category.id}}">
+    <a href="/budgets/{{category.budgetId}}/categories/{{category.id}}">
         <div class="row" style="justify-content: space-between">
             <span class="body-large">{{category.title}}</span>
             <span class="body-small">{{remainingAmountLabel}} remaining</span>
diff --git a/web/src/main/resources/templates/partials/transaction-list.mustache b/web/src/main/resources/templates/partials/transaction-list.mustache
new file mode 100644
index 0000000..dba41f1
--- /dev/null
+++ b/web/src/main/resources/templates/partials/transaction-list.mustache
@@ -0,0 +1,18 @@
+<li class="list-item">
+    <h5>
+        {{key}}
+    </h5>
+</li>
+{{#value}}
+    <li class="list-item">
+        <a href="/budgets/{{budgetId}}/transactions/{{id}}">
+            <div class="row" style="justify-content: space-between">
+                <div class="column">
+                    <span class="body-large">{{title}}</span>
+                    <span class="body-small">{{description}}</span>
+                </div>
+                <span class="body-medium {{expenseClass}}">{{amountLabel}}</span>
+            </div>
+        </a>
+    </li>
+{{/value}}
\ No newline at end of file