diff --git a/backend/src/db/mod.rs b/backend/src/db/mod.rs
index ff008f8..b4f3399 100644
--- a/backend/src/db/mod.rs
+++ b/backend/src/db/mod.rs
@@ -9,4 +9,5 @@ pub mod sessions;
 pub mod settings;
 pub mod sources;
 pub mod syntheses;
+pub mod themes;
 pub mod users;
diff --git a/backend/src/db/themes.rs b/backend/src/db/themes.rs
new file mode 100644
index 0000000..5529b97
--- /dev/null
+++ b/backend/src/db/themes.rs
@@ -0,0 +1,106 @@
+//! Database queries for the `themes` table.
+
+use sqlx::PgPool;
+use uuid::Uuid;
+
+use crate::errors::AppError;
+use crate::models::theme::Theme;
+
+pub async fn list_for_user(pool: &PgPool, user_id: Uuid) -> Result<Vec<Theme>, AppError> {
+    let themes = sqlx::query_as::<_, Theme>(
+        "SELECT * FROM themes WHERE user_id = $1 ORDER BY created_at ASC"
+    )
+    .bind(user_id)
+    .fetch_all(pool)
+    .await?;
+    Ok(themes)
+}
+
+pub async fn get_by_id(pool: &PgPool, user_id: Uuid, id: Uuid) -> Result<Option<Theme>, AppError> {
+    let theme = sqlx::query_as::<_, Theme>(
+        "SELECT * FROM themes WHERE id = $1 AND user_id = $2"
+    )
+    .bind(id)
+    .bind(user_id)
+    .fetch_optional(pool)
+    .await?;
+    Ok(theme)
+}
+
+pub async fn create(
+    pool: &PgPool,
+    user_id: Uuid,
+    name: &str,
+    theme: &str,
+    categories: &serde_json::Value,
+    max_items_per_category: i32,
+    max_age_days: i32,
+    summary_length: i32,
+) -> Result<Theme, AppError> {
+    let row = sqlx::query_as::<_, Theme>(
+        r#"
+        INSERT INTO themes (user_id, name, theme, categories, max_items_per_category, max_age_days, summary_length)
+        VALUES ($1, $2, $3, $4, $5, $6, $7)
+        RETURNING *
+        "#,
+    )
+    .bind(user_id)
+    .bind(name)
+    .bind(theme)
+    .bind(categories)
+    .bind(max_items_per_category)
+    .bind(max_age_days)
+    .bind(summary_length)
+    .fetch_one(pool)
+    .await?;
+    Ok(row)
+}
+
+pub async fn update(
+    pool: &PgPool,
+    user_id: Uuid,
+    id: Uuid,
+    name: Option<&str>,
+    theme: Option<&str>,
+    categories: Option<&serde_json::Value>,
+    max_items_per_category: Option<i32>,
+    max_age_days: Option<i32>,
+    summary_length: Option<i32>,
+) -> Result<Option<Theme>, AppError> {
+    let row = sqlx::query_as::<_, Theme>(
+        r#"
+        UPDATE themes SET
+            name = COALESCE($3, name),
+            theme = COALESCE($4, theme),
+            categories = COALESCE($5, categories),
+            max_items_per_category = COALESCE($6, max_items_per_category),
+            max_age_days = COALESCE($7, max_age_days),
+            summary_length = COALESCE($8, summary_length),
+            updated_at = now()
+        WHERE id = $1 AND user_id = $2
+        RETURNING *
+        "#,
+    )
+    .bind(id)
+    .bind(user_id)
+    .bind(name)
+    .bind(theme)
+    .bind(categories)
+    .bind(max_items_per_category)
+    .bind(max_age_days)
+    .bind(summary_length)
+    .fetch_optional(pool)
+    .await?;
+    Ok(row)
+}
+
+pub async fn delete(pool: &PgPool, user_id: Uuid, id: Uuid) -> Result<bool, AppError> {
+    let result = sqlx::query(
+        "DELETE FROM themes WHERE id = $1 AND user_id = $2"
+    )
+    .bind(id)
+    .bind(user_id)
+    .execute(pool)
+    .await?;
+    Ok(result.rows_affected() > 0)
+}
diff --git a/backend/src/models/mod.rs b/backend/src/models/mod.rs
index 807616d..883c058 100644
--- a/backend/src/models/mod.rs
+++ b/backend/src/models/mod.rs
@@ -7,4 +7,5 @@ pub mod session;
 pub mod settings;
 pub mod source;
 pub mod synthesis;
+pub mod theme;
 pub mod user;
diff --git a/backend/src/models/theme.rs b/backend/src/models/theme.rs
new file mode 100644
index 0000000..9544c55
--- /dev/null
+++ b/backend/src/models/theme.rs
@@ -0,0 +1,117 @@
+//! Theme model — per-topic content settings.
+
+use chrono::{DateTime, Utc};
+use serde::{Deserialize, Serialize};
+use uuid::Uuid;
+
+use crate::errors::AppError;
+
+/// A user's theme with content settings.
+#[derive(Debug, Clone, Serialize, sqlx::FromRow)]
+pub struct Theme {
+    pub id: Uuid,
+    pub user_id: Uuid,
+    pub name: String,
+    pub theme: String,
+    pub categories: serde_json::Value,
+    pub max_items_per_category: i32,
+    pub max_age_days: i32,
+    pub summary_length: i32,
+    pub created_at: DateTime<Utc>,
+    pub updated_at: DateTime<Utc>,
+}
+
+/// Request body for creating a theme.
+#[derive(Debug, Deserialize)]
+pub struct CreateThemeRequest {
+    pub name: String,
+    pub theme: String,
+    pub categories: Vec<String>,
+    pub max_items_per_category: Option<i32>,
+    pub max_age_days: Option<i32>,
+    pub summary_length: Option<i32>,
+}
+
+impl CreateThemeRequest {
+    pub fn validate(&self) -> Result<(), String> {
+        if self.name.trim().is_empty() {
+            return Err("Theme name cannot be empty".into());
+        }
+        if self.name.len() > 200 {
+            return Err("Theme name must be at most 200 characters".into());
+        }
+        if self.theme.trim().is_empty() {
+            return Err("Theme search topic cannot be empty".into());
+        }
+        if self.categories.is_empty() {
+            return Err("Categories cannot be empty".into());
+        }
+        if self.categories.len() > 20 {
+            return Err("At most 20 categories are allowed".into());
+        }
+        for (i, cat) in self.categories.iter().enumerate() {
+            if cat.trim().is_empty() {
+                return Err(format!("Category at index {} cannot be empty", i));
+            }
+        }
+        if let Some(max) = self.max_items_per_category {
+            if !(1..=50).contains(&max) {
+                return Err("max_items_per_category must be between 1 and 50".into());
+            }
+        }
+        if let Some(days) = self.max_age_days {
+            if !(1..=365).contains(&days) {
+                return Err("max_age_days must be between 1 and 365".into());
+            }
+        }
+        if let Some(sl) = self.summary_length {
+            if !(1..=3).contains(&sl) {
+                return Err("summary_length must be between 1 and 3".into());
+            }
+        }
+        Ok(())
+    }
+}
+
+/// Request body for updating a theme.
+#[derive(Debug, Deserialize)]
+pub struct UpdateThemeRequest {
+    pub name: Option<String>,
+    pub theme: Option<String>,
+    pub categories: Option<Vec<String>>,
+    pub max_items_per_category: Option<i32>,
+    pub max_age_days: Option<i32>,
+    pub summary_length: Option<i32>,
+}
+
+/// Response shape for theme API.
+#[derive(Debug, Serialize)]
+pub struct ThemeResponse {
+    pub id: Uuid,
+    pub name: String,
+    pub theme: String,
+    pub categories: Vec<String>,
+    pub max_items_per_category: i32,
+    pub max_age_days: i32,
+    pub summary_length: i32,
+    pub created_at: DateTime<Utc>,
+    pub updated_at: DateTime<Utc>,
+}
+
+impl TryFrom<Theme> for ThemeResponse {
+    type Error = AppError;
+    fn try_from(t: Theme) -> Result<Self, Self::Error> {
+        let categories: Vec<String> = serde_json::from_value(t.categories).unwrap_or_default();
+        Ok(Self {
+            id: t.id,
+            name: t.name,
+            theme: t.theme,
+            categories,
+            max_items_per_category: t.max_items_per_category,
+            max_age_days: t.max_age_days,
+            summary_length: t.summary_length,
+            created_at: t.created_at,
+            updated_at: t.updated_at,
+        })
+    }
+}