diff --git a/CHANGES.md b/CHANGES.md
index 74aa2fa..593e047 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,5 +1,8 @@
 ## 0.6.0 In development
 
+* Convert seq param values to literal sql param lists (@dball)
+* Apply seq to sets when converting to sql (@dball)
+
 ## 0.5.3
 
 * Support exists syntax (@cddr)
diff --git a/src/honeysql/format.clj b/src/honeysql/format.clj
index 8031484..fcdcf63 100644
--- a/src/honeysql/format.clj
+++ b/src/honeysql/format.clj
@@ -248,10 +248,24 @@
         (into [sql-str] @*params*)
         [sql-str]))))
 
+(defprotocol Parameterizable
+  (to-params [value pname]))
+
+(extend-protocol Parameterizable
+  clojure.lang.Sequential
+  (to-params [value pname]
+    (paren-wrap (comma-join (mapv #(to-params % pname) value))))
+  clojure.lang.IPersistentSet
+  (to-params [value pname]
+    (to-params (seq value) pname))
+  java.lang.Object
+  (to-params [value pname]
+    (swap! *params* conj value)
+    (swap! *param-names* conj pname)
+    (*parameterizer*)))
+
 (defn add-param [pname pval]
-  (swap! *param-names* conj pname)
-  (swap! *params* conj pval)
-  (*parameterizer*))
+  (to-params pval pname))
 
 ;; Anonymous param name -- :_1, :_2, etc.
 (defn add-anon-param [pval]
@@ -320,6 +334,9 @@
       (if *subquery?*
         (paren-wrap sql-str)
         sql-str)))
+  clojure.lang.IPersistentSet
+  (-to-sql [x]
+    (-to-sql (seq x)))
   nil
   (-to-sql [x] "NULL")
   SqlParam
diff --git a/test/honeysql/core_test.clj b/test/honeysql/core_test.clj
index b465411..9545bb7 100644
--- a/test/honeysql/core_test.clj
+++ b/test/honeysql/core_test.clj
@@ -80,3 +80,39 @@
            (columns :bar)
            (values [[(honeysql.format/value {:baz "my-val"})]])
            sql/format))))
+
+(deftest test-operators
+  (testing "in"
+    (doseq [[cname coll] [[:vector []] [:set #{}] [:list '()]]]
+      (testing (str "with values from a " (name cname))
+        (let [values (conj coll 1)]
+          (is (= ["SELECT * FROM customers WHERE (id in (1))"]
+                 (sql/format {:select [:*]
+                              :from [:customers]
+                              :where [:in :id values]})))
+          (is (= ["SELECT * FROM customers WHERE (id in (?))" 1]
+                 (sql/format {:select [:*]
+                              :from [:customers]
+                              :where [:in :id :?ids]}
+                             {:ids values}))))))
+    (testing "with more than one integer"
+      (let [values [1 2]]
+        (is (= ["SELECT * FROM customers WHERE (id in (1, 2))"]
+               (sql/format {:select [:*]
+                            :from [:customers]
+                            :where [:in :id values]})))
+        (is (= ["SELECT * FROM customers WHERE (id in (?, ?))" 1 2]
+               (sql/format {:select [:*]
+                            :from [:customers]
+                            :where [:in :id :?ids]}
+                           {:ids values})))))
+    (testing "with more than one string"
+      (let [values ["1" "2"]]
+        (is (= ["SELECT * FROM customers WHERE (id in (?, ?))" "1" "2"]
+               (sql/format {:select [:*]
+                            :from [:customers]
+                            :where [:in :id values]})
+               (sql/format {:select [:*]
+                            :from [:customers]
+                            :where [:in :id :?ids]}
+                           {:ids values})))))))