diff --git a/cli/src/cmd/debug.rs b/cli/src/cmd/debug.rs
new file mode 100644
index 000000000..f81f605b7
--- /dev/null
+++ b/cli/src/cmd/debug.rs
@@ -0,0 +1,57 @@
+use crate::table;
+use clap::{App, ArgMatches, SubCommand as ClapSubCommand};
+use failure::Fallible;
+use prettytable::{cell, row, Table};
+
+use crate::cmd::{shared, ArgMatchResult, CommandInvocation};
+
+#[derive(Debug)]
+struct Invocation {
+    task: String,
+}
+
+define_subcommand! {
+    fn decorate_app<'a>(&self, app: App<'a, 'a>) -> App<'a, 'a> {
+        app.subcommand(
+            ClapSubCommand::with_name("debug")
+                .about("debug info for the given task")
+                .arg(shared::task_arg()))
+    }
+
+    fn arg_match<'a>(&self, matches: &ArgMatches<'a>) -> ArgMatchResult {
+        match matches.subcommand() {
+            ("debug", Some(matches)) => ArgMatchResult::Ok(Box::new(Invocation {
+                task: matches.value_of("task").unwrap().into(),
+            })),
+            _ => ArgMatchResult::None,
+        }
+    }
+}
+
+subcommand_invocation! {
+    fn run(&self, command: &CommandInvocation) -> Fallible<()> {
+        let mut replica = command.get_replica();
+        let task = shared::get_task(&mut replica, &self.task)?;
+
+        let mut t = Table::new();
+        t.set_format(table::format());
+        t.set_titles(row![b->"key", b->"value"]);
+        for (k, v) in task.get_taskmap().iter() {
+            t.add_row(row![k, v]);
+        }
+        t.printstd();
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn parse_command() {
+        with_subcommand_invocation!(vec!["task", "debug", "1"], |inv: &Invocation| {
+            assert_eq!(inv.task, "1".to_string());
+        });
+    }
+}
diff --git a/cli/src/cmd/info.rs b/cli/src/cmd/info.rs
index f55667dfb..919e47a76 100644
--- a/cli/src/cmd/info.rs
+++ b/cli/src/cmd/info.rs
@@ -42,6 +42,7 @@ subcommand_invocation! {
         }
         t.add_row(row![b->"Description", task.get_description()]);
         t.add_row(row![b->"Status", task.get_status()]);
+        t.add_row(row![b->"Active", task.is_active()]);
         t.printstd();
         Ok(())
     }
diff --git a/cli/src/cmd/list.rs b/cli/src/cmd/list.rs
index 72ee206e0..4dddd5265 100644
--- a/cli/src/cmd/list.rs
+++ b/cli/src/cmd/list.rs
@@ -26,13 +26,17 @@ subcommand_invocation! {
         let mut replica = command.get_replica()?;
         let mut t = Table::new();
         t.set_format(table::format());
-        t.set_titles(row![b->"id", b->"description"]);
+        t.set_titles(row![b->"id", b->"act", b->"description"]);
         for (uuid, task) in replica.all_tasks().unwrap() {
             let mut id = uuid.to_string();
             if let Some(i) = replica.get_working_set_index(&uuid)? {
                 id = i.to_string();
             }
-            t.add_row(row![id, task.get_description()]);
+            let active = match task.is_active() {
+                true => "*",
+                false => "",
+            };
+            t.add_row(row![id, active, task.get_description()]);
         }
         t.printstd();
         Ok(())
diff --git a/cli/src/cmd/mod.rs b/cli/src/cmd/mod.rs
index 2705c90c0..d58237816 100644
--- a/cli/src/cmd/mod.rs
+++ b/cli/src/cmd/mod.rs
@@ -6,22 +6,28 @@ mod macros;
 mod shared;
 
 mod add;
+mod debug;
 mod gc;
 mod info;
 mod list;
 mod modify;
 mod pending;
+mod start;
+mod stop;
 mod sync;
 
 /// Get a list of all subcommands in this crate
 pub(crate) fn subcommands() -> Vec<Box<dyn SubCommand>> {
     vec![
         add::cmd(),
+        debug::cmd(),
         gc::cmd(),
         info::cmd(),
         list::cmd(),
         modify::cmd(),
         pending::cmd(),
+        start::cmd(),
+        stop::cmd(),
         sync::cmd(),
     ]
 }
diff --git a/cli/src/cmd/pending.rs b/cli/src/cmd/pending.rs
index f35756b8b..f4f99974a 100644
--- a/cli/src/cmd/pending.rs
+++ b/cli/src/cmd/pending.rs
@@ -28,10 +28,14 @@ subcommand_invocation! {
         let working_set = command.get_replica()?.working_set().unwrap();
         let mut t = Table::new();
         t.set_format(table::format());
-        t.set_titles(row![b->"id", b->"description"]);
+        t.set_titles(row![b->"id", b->"act", b->"description"]);
         for (i, item) in working_set.iter().enumerate() {
             if let Some(ref task) = item {
-                t.add_row(row![i, task.get_description()]);
+                let active = match task.is_active() {
+                    true => "*",
+                    false => "",
+                };
+                t.add_row(row![i, active, task.get_description()]);
             }
         }
         t.printstd();
diff --git a/cli/src/cmd/start.rs b/cli/src/cmd/start.rs
new file mode 100644
index 000000000..95365003c
--- /dev/null
+++ b/cli/src/cmd/start.rs
@@ -0,0 +1,48 @@
+use clap::{App, ArgMatches, SubCommand as ClapSubCommand};
+use failure::Fallible;
+
+use crate::cmd::{shared, ArgMatchResult, CommandInvocation};
+
+#[derive(Debug)]
+struct Invocation {
+    task: String,
+}
+
+define_subcommand! {
+    fn decorate_app<'a>(&self, app: App<'a, 'a>) -> App<'a, 'a> {
+        app.subcommand(
+            ClapSubCommand::with_name("start")
+                .about("start the given task")
+                .arg(shared::task_arg()))
+    }
+
+    fn arg_match<'a>(&self, matches: &ArgMatches<'a>) -> ArgMatchResult {
+        match matches.subcommand() {
+            ("start", Some(matches)) => ArgMatchResult::Ok(Box::new(Invocation {
+                task: matches.value_of("task").unwrap().into(),
+            })),
+            _ => ArgMatchResult::None,
+        }
+    }
+}
+
+subcommand_invocation! {
+    fn run(&self, command: &CommandInvocation) -> Fallible<()> {
+        let mut replica = command.get_replica();
+        let task = shared::get_task(&mut replica, &self.task)?;
+        task.into_mut(&mut replica).start()?;
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn parse_command() {
+        with_subcommand_invocation!(vec!["task", "start", "1"], |inv: &Invocation| {
+            assert_eq!(inv.task, "1".to_string());
+        });
+    }
+}
diff --git a/cli/src/cmd/stop.rs b/cli/src/cmd/stop.rs
new file mode 100644
index 000000000..d61eb8b51
--- /dev/null
+++ b/cli/src/cmd/stop.rs
@@ -0,0 +1,48 @@
+use clap::{App, ArgMatches, SubCommand as ClapSubCommand};
+use failure::Fallible;
+
+use crate::cmd::{shared, ArgMatchResult, CommandInvocation};
+
+#[derive(Debug)]
+struct Invocation {
+    task: String,
+}
+
+define_subcommand! {
+    fn decorate_app<'a>(&self, app: App<'a, 'a>) -> App<'a, 'a> {
+        app.subcommand(
+            ClapSubCommand::with_name("stop")
+                .about("stop the given task")
+                .arg(shared::task_arg()))
+    }
+
+    fn arg_match<'a>(&self, matches: &ArgMatches<'a>) -> ArgMatchResult {
+        match matches.subcommand() {
+            ("stop", Some(matches)) => ArgMatchResult::Ok(Box::new(Invocation {
+                task: matches.value_of("task").unwrap().into(),
+            })),
+            _ => ArgMatchResult::None,
+        }
+    }
+}
+
+subcommand_invocation! {
+    fn run(&self, command: &CommandInvocation) -> Fallible<()> {
+        let mut replica = command.get_replica();
+        let task = shared::get_task(&mut replica, &self.task)?;
+        task.into_mut(&mut replica).stop()?;
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn parse_command() {
+        with_subcommand_invocation!(vec!["task", "stop", "1"], |inv: &Invocation| {
+            assert_eq!(inv.task, "1".to_string());
+        });
+    }
+}
diff --git a/docs/src/tasks.md b/docs/src/tasks.md
index 5727237dc..d53715bbd 100644
--- a/docs/src/tasks.md
+++ b/docs/src/tasks.md
@@ -30,6 +30,7 @@ The following keys, and key formats, are defined:
 * `status` - one of `P` for a pending task (the default), `C` for completed or `D` for deleted
 * `description` - the one-line summary of the task
 * `modified` - the time of the last modification of this task
+* `start.<timestamp>` - either an empty string (representing work on the task to the task that has not been stopped) or a timestamp (representing the time that work stopped)
 
 The following are not yet implemented:
 
diff --git a/taskchampion/src/task.rs b/taskchampion/src/task.rs
index 332eb57b1..a5569161c 100644
--- a/taskchampion/src/task.rs
+++ b/taskchampion/src/task.rs
@@ -118,6 +118,10 @@ impl Task {
         &self.uuid
     }
 
+    pub fn get_taskmap(&self) -> &TaskMap {
+        &self.taskmap
+    }
+
     /// Prepare to mutate this task, requiring a mutable Replica
     /// in order to update the data it contains.
     pub fn into_mut(self, replica: &mut Replica) -> TaskMut {
@@ -142,6 +146,16 @@ impl Task {
             .unwrap_or("")
     }
 
+    /// Determine whether this task is active -- that is, that it has been started
+    /// and not stopped.
+    pub fn is_active(&self) -> bool {
+        self.taskmap
+            .iter()
+            .filter(|(k, v)| k.starts_with("start.") && v.is_empty())
+            .next()
+            .is_some()
+    }
+
     pub fn get_modified(&self) -> Option<DateTime<Utc>> {
         self.get_timestamp("modified")
     }
@@ -184,6 +198,33 @@ impl<'r> TaskMut<'r> {
         self.set_timestamp("modified", Some(modified))
     }
 
+    /// Start the task by creating "start.<timestamp": "", if the task is not already
+    /// active.
+    pub fn start(&mut self) -> Fallible<()> {
+        if self.is_active() {
+            return Ok(());
+        }
+        let k = format!("start.{}", Utc::now().timestamp());
+        self.set_string(k.as_ref(), Some(String::from("")))
+    }
+
+    /// Stop the task by adding the current timestamp to all un-resolved "start.<timestamp>" keys.
+    pub fn stop(&mut self) -> Fallible<()> {
+        let keys = self
+            .taskmap
+            .iter()
+            .filter(|(k, v)| k.starts_with("start.") && v.is_empty())
+            .map(|(k, _)| k)
+            .cloned()
+            .collect::<Vec<_>>();
+        let now = Utc::now();
+        for key in keys {
+            println!("{}", key);
+            self.set_timestamp(&key, Some(now))?;
+        }
+        Ok(())
+    }
+
     // -- utility functions
 
     fn lastmod(&mut self) -> Fallible<()> {
@@ -212,11 +253,26 @@ impl<'r> TaskMut<'r> {
 
     fn set_timestamp(&mut self, property: &str, value: Option<DateTime<Utc>>) -> Fallible<()> {
         self.lastmod()?;
-        self.replica.update_task(
-            self.task.uuid,
-            property,
-            value.map(|v| format!("{}", v.timestamp())),
-        )
+        if let Some(value) = value {
+            let ts = format!("{}", value.timestamp());
+            self.replica
+                .update_task(self.task.uuid, property, Some(ts.clone()))?;
+            self.task.taskmap.insert(property.to_string(), ts);
+        } else {
+            self.replica
+                .update_task::<_, &str>(self.task.uuid, property, None)?;
+            self.task.taskmap.remove(property);
+        }
+        Ok(())
+    }
+
+    /// Used by tests to ensure that updates are properly written
+    #[cfg(test)]
+    fn reload(&mut self) -> Fallible<()> {
+        let uuid = self.uuid;
+        let task = self.replica.get_task(&uuid)?.unwrap();
+        self.task.taskmap = task.taskmap;
+        Ok(())
     }
 }
 
@@ -232,6 +288,132 @@ impl<'r> std::ops::Deref for TaskMut<'r> {
 mod test {
     use super::*;
 
+    fn with_mut_task<F: FnOnce(TaskMut)>(f: F) {
+        let mut replica = Replica::new_inmemory();
+        let task = replica.new_task(Status::Pending, "test".into()).unwrap();
+        let task = task.into_mut(&mut replica);
+        f(task)
+    }
+
+    #[test]
+    fn test_is_active_never_started() {
+        let task = Task::new(Uuid::new_v4(), TaskMap::new());
+        assert!(!task.is_active());
+    }
+
+    #[test]
+    fn test_is_active() {
+        let task = Task::new(
+            Uuid::new_v4(),
+            vec![(String::from("start.1234"), String::from(""))]
+                .drain(..)
+                .collect(),
+        );
+
+        assert!(task.is_active());
+    }
+
+    #[test]
+    fn test_is_active_stopped() {
+        let task = Task::new(
+            Uuid::new_v4(),
+            vec![(String::from("start.1234"), String::from("1235"))]
+                .drain(..)
+                .collect(),
+        );
+
+        assert!(!task.is_active());
+    }
+
+    fn count_taskmap(task: &TaskMut, f: fn(&(&String, &String)) -> bool) -> usize {
+        task.taskmap.iter().filter(f).count()
+    }
+
+    #[test]
+    fn test_start() {
+        with_mut_task(|mut task| {
+            task.start().unwrap();
+            assert_eq!(
+                count_taskmap(&task, |(k, v)| k.starts_with("start.") && v.is_empty()),
+                1
+            );
+            task.reload().unwrap();
+            assert_eq!(
+                count_taskmap(&task, |(k, v)| k.starts_with("start.") && v.is_empty()),
+                1
+            );
+
+            // second start doesn't change anything..
+            task.start().unwrap();
+            assert_eq!(
+                count_taskmap(&task, |(k, v)| k.starts_with("start.") && v.is_empty()),
+                1
+            );
+            task.reload().unwrap();
+            assert_eq!(
+                count_taskmap(&task, |(k, v)| k.starts_with("start.") && v.is_empty()),
+                1
+            );
+        });
+    }
+
+    #[test]
+    fn test_stop() {
+        with_mut_task(|mut task| {
+            task.start().unwrap();
+            task.stop().unwrap();
+            assert_eq!(
+                count_taskmap(&task, |(k, v)| k.starts_with("start.") && v.is_empty()),
+                0
+            );
+            assert_eq!(
+                count_taskmap(&task, |(k, v)| k.starts_with("start.") && !v.is_empty()),
+                1
+            );
+            task.reload().unwrap();
+            assert_eq!(
+                count_taskmap(&task, |(k, v)| k.starts_with("start.") && v.is_empty()),
+                0
+            );
+            assert_eq!(
+                count_taskmap(&task, |(k, v)| k.starts_with("start.") && !v.is_empty()),
+                1
+            );
+        });
+    }
+
+    #[test]
+    fn test_stop_multiple() {
+        with_mut_task(|mut task| {
+            // simulate a task that has (through the synchronization process) been started twice
+            task.task
+                .taskmap
+                .insert(String::from("start.1234"), String::from(""));
+            task.task
+                .taskmap
+                .insert(String::from("start.5678"), String::from(""));
+
+            task.stop().unwrap();
+            assert_eq!(
+                count_taskmap(&task, |(k, v)| k.starts_with("start.") && v.is_empty()),
+                0
+            );
+            assert_eq!(
+                count_taskmap(&task, |(k, v)| k.starts_with("start.") && !v.is_empty()),
+                2
+            );
+            task.reload().unwrap();
+            assert_eq!(
+                count_taskmap(&task, |(k, v)| k.starts_with("start.") && v.is_empty()),
+                0
+            );
+            assert_eq!(
+                count_taskmap(&task, |(k, v)| k.starts_with("start.") && !v.is_empty()),
+                2
+            );
+        });
+    }
+
     #[test]
     fn test_priority() {
         assert_eq!(Priority::L.to_taskmap(), "L");