diff --git a/notes.txt b/notes.txt
index 4c996ec..0df6b0f 100644
--- a/notes.txt
+++ b/notes.txt
@@ -293,3 +293,22 @@ SELECT failures.* FROM failures
 		ON failures.task_result_id = task_results.id
 	WHERE
 		task_results.operation = :operation
+
+
+==================
+
+task_states
+	all task_results, with is_candidate precalculated
+
+dependency_task_states
+	all task_states for tasks+versions listed in :dependencyTasks
+
+candidates (items which are *permitted* to be run)
+	all tag-relevant items which are not listed as "in progress", and for which all dependency tasks have been satisfied
+		all dependency tasks have been satisfied = NOT EXISTS ( join(dependencyTasks, task_states on task/version and where item_id) where is_candidate is null or true )
+
+results (items which *should* be run, in order of preference)
+	all candidates (item + task_result) for which there is either:
+		1. no entry in task_states
+		2. an is_candidate=TRUE entry in task_states
+		3. an entry in task_states with mismatching task_version
diff --git a/src/kernel.js b/src/kernel.js
index 6d0dbbb..302ab54 100644
--- a/src/kernel.js
+++ b/src/kernel.js
@@ -95,7 +95,13 @@ module.exports = function createKernel(configuration) {
 							: null,
 						globalParallelize: (configuration.parallelTasks != null)
 							? parallelize(configuration.parallelTasks)
-							: null
+							: null,
+						taskDependencies: defaultValue(taskConfiguration.dependsOn, []).map((task) => {
+							return {
+								task: task,
+								taskVersion: defaultValue(configuration.tasks[task].taskVersion, "0")
+							};
+						})
 					});
 
 					return pipe([
@@ -107,6 +113,9 @@ module.exports = function createKernel(configuration) {
 				} else {
 					throw new Error(`Task '${task}' is defined to run for tags [${tags}], but no such task is defined`);
 				}
+			}).catch((error) => {
+				console.dir(error, { depth: null, colors: true });
+				throw error;
 			});
 		}
 		
diff --git a/src/task-stream.js b/src/task-stream.js
index 6ac4a9b..2402418 100644
--- a/src/task-stream.js
+++ b/src/task-stream.js
@@ -13,38 +13,68 @@ const pipe = require("@promistream/pipe");
 const createMutationAPIWrapper = require("./mutation-api/wrapper");
 
 let query = `
-	WITH candidates AS (
+	WITH
+		dependency_tasks AS (
+			SELECT * FROM
+				json_to_recordset(:dependencyTaskDefinitions) AS x(task text, task_version text)
+		),
+		task_states AS (
+			SELECT
+				*,
+				(
+					is_successful = TRUE
+					AND (
+						expires_at < NOW()
+						OR is_invalidated = TRUE
+					)
+				) AS is_candidate
+			FROM task_results
+		),
+		matching_items AS (
+			SELECT
+				DISTINCT ON (items.id)
+				items.*,
+				states.updated_at AS result_date,
+				states.is_candidate,
+				states.task_version
+			FROM items
+				INNER JOIN tags
+					ON tags.item_id = items.id
+					AND tags.name = ANY(:tags)
+				LEFT JOIN task_states AS states
+					ON states.item_id = items.id
+					AND states.task = :task
+				WHERE
+					NOT EXISTS (
+						SELECT FROM tasks_in_progress AS pr WHERE pr.item_id = items.id
+					)
+		),
+		candidates AS (
+			SELECT * FROM matching_items
+				WHERE result_date IS NULL
+			UNION
+			SELECT * FROM matching_items
+				WHERE is_candidate = TRUE
+				OR NOT (task_version = :taskVersion)
+		)
+	(
 		SELECT
-			DISTINCT ON (items.id)
-			items.*,
-			results.expires_at,
-			results.is_invalidated,
-			results.is_successful,
-			results.updated_at AS result_date,
-			results.task_version
-		FROM items
-			INNER JOIN tags
-				ON tags.item_id = items.id
-				AND tags.name = ANY(:tags)
-			LEFT JOIN task_results AS results
-				ON results.item_id = items.id
-				AND results.task = :task
-			WHERE NOT EXISTS (
-				SELECT FROM tasks_in_progress AS pr WHERE pr.item_id = items.id
+			*
+		FROM
+			candidates
+		WHERE
+			NOT EXISTS (
+				SELECT
+					task_states.*
+				FROM dependency_tasks
+					LEFT JOIN task_states
+						ON dependency_tasks.task = task_states.task
+						AND dependency_tasks.task_version = task_states.task_version
+						AND task_states.item_id = candidates.id
+				WHERE
+					task_states.is_candidate IS NULL
+					OR task_states.is_candidate = TRUE
 			)
-	)
-	(
-		SELECT * FROM candidates
-			WHERE result_date IS NULL
-		UNION
-		SELECT * FROM candidates
-			WHERE
-				is_successful = TRUE
-				AND (
-					expires_at < NOW()
-					OR is_invalidated = TRUE
-					OR NOT (task_version = :taskVersion)
-				)
 	) LIMIT :resultLimit;
 `;
 
@@ -57,7 +87,7 @@ module.exports = function (state) {
 
 	// FIXME: Transaction support!
 	
-	return function createTaskStream({ task, taskVersion, tags, run, ttl, globalRateLimiter, globalParallelize }) {
+	return function createTaskStream({ task, taskVersion, taskDependencies, tags, run, ttl, globalRateLimiter, globalParallelize }) {
 		// TODO: Make nicer
 		let ttlInSeconds = (ttl != null)
 			? (typeof ttl === "number")
@@ -75,12 +105,13 @@ module.exports = function (state) {
 						tags: tags,
 						task: task,
 						taskVersion: taskVersion,
-						resultLimit: 1000 // TODO: Make configurable
+						resultLimit: 1000, // TODO: Make configurable
+						dependencyTaskDefinitions: JSON.stringify(taskDependencies)
 					});
 				}).then((result) => {
 					let timeElapsed = Date.now() - startTime;
 
-					debug(`Task retrieval query took ${timeElapsed}ms and produced ${result.rowCount} results`);
+					debug(`Task retrieval query for '${task}' took ${timeElapsed}ms and produced ${result.rowCount} results`);
 
 					if (result.rowCount > 0) {
 						// console.log("rows:", result.rows);