diff --git a/src/lib.rs b/src/lib.rs
index c2c80cfef..7ec4cd83c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -3,6 +3,7 @@
 
 mod errors;
 mod operation;
+mod replica;
 mod server;
 mod taskdb;
 
diff --git a/src/replica.rs b/src/replica.rs
new file mode 100644
index 000000000..c0b147997
--- /dev/null
+++ b/src/replica.rs
@@ -0,0 +1,99 @@
+use crate::errors::Error;
+use crate::operation::Operation;
+use crate::taskdb::DB;
+use chrono::Utc;
+use std::collections::HashMap;
+use uuid::Uuid;
+
+/// A replica represents an instance of a user's task data.
+struct Replica {
+    taskdb: Box<DB>,
+}
+
+impl Replica {
+    pub fn new(taskdb: Box<DB>) -> Replica {
+        return Replica { taskdb };
+    }
+
+    /// Create a new task.  The task must not already exist.
+    pub fn create_task(&mut self, uuid: Uuid) -> Result<(), Error> {
+        self.taskdb.apply(Operation::Create { uuid })
+    }
+
+    /// Delete a task.  The task must exist.
+    pub fn delete_task(&mut self, uuid: Uuid) -> Result<(), Error> {
+        self.taskdb.apply(Operation::Delete { uuid })
+    }
+
+    /// Update an existing task.  If the value is Some, the property is added or updated.  If the
+    /// value is None, the property is deleted.  It is not an error to delete a nonexistent
+    /// property.
+    pub fn update_task<S1, S2>(
+        &mut self,
+        uuid: Uuid,
+        property: S1,
+        value: Option<S2>,
+    ) -> Result<(), Error>
+    where
+        S1: Into<String>,
+        S2: Into<String>,
+    {
+        self.taskdb.apply(Operation::Update {
+            uuid,
+            property: property.into(),
+            value: value.map(|v| v.into()),
+            timestamp: Utc::now(),
+        })
+    }
+
+    /// Get an existing task by its UUID
+    pub fn get_task(&self, uuid: &Uuid) -> Option<&HashMap<String, String>> {
+        self.taskdb.tasks().get(&uuid)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::taskdb::DB;
+    use uuid::Uuid;
+
+    #[test]
+    fn create() {
+        let mut rep = Replica::new(DB::new().into());
+        let uuid = Uuid::new_v4();
+
+        rep.create_task(uuid.clone()).unwrap();
+        assert_eq!(rep.get_task(&uuid), Some(&HashMap::new()));
+    }
+
+    #[test]
+    fn delete() {
+        let mut rep = Replica::new(DB::new().into());
+        let uuid = Uuid::new_v4();
+
+        rep.create_task(uuid.clone()).unwrap();
+        rep.delete_task(uuid.clone()).unwrap();
+        assert_eq!(rep.get_task(&uuid), None);
+    }
+
+    #[test]
+    fn update() {
+        let mut rep = Replica::new(DB::new().into());
+        let uuid = Uuid::new_v4();
+
+        rep.create_task(uuid.clone()).unwrap();
+        rep.update_task(uuid.clone(), "title", Some("snarsblat"))
+            .unwrap();
+        let mut task = HashMap::new();
+        task.insert("title".into(), "snarsblat".into());
+        assert_eq!(rep.get_task(&uuid), Some(&task));
+    }
+
+    #[test]
+    fn get_does_not_exist() {
+        let rep = Replica::new(DB::new().into());
+        let uuid = Uuid::new_v4();
+        assert_eq!(rep.get_task(&uuid), None);
+    }
+}
diff --git a/src/taskdb.rs b/src/taskdb.rs
index 1c1cec9e9..34506450d 100644
--- a/src/taskdb.rs
+++ b/src/taskdb.rs
@@ -39,9 +39,9 @@ impl DB {
         }
     }
 
-    /// Apply an operation to the DB.  Aside from synchronization operations, this
-    /// is the only way to modify the DB.  In cases where an operation does not
-    /// make sense, this function will ignore the operation.
+    /// Apply an operation to the DB.  Aside from synchronization operations, this is the only way
+    /// to modify the DB.  In cases where an operation does not make sense, this function will do
+    /// nothing and return an error (but leave the DB in a consistent state).
     pub fn apply(&mut self, op: Operation) -> Result<(), Error> {
         if let err @ Err(_) = self.apply_op(&op) {
             return err;