diff --git a/CHANGELOG.md b/CHANGELOG.md
index b6e5edb..2420cab 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,7 @@
 # Changes
 
 * 2.3.next in progress
+  * Address [#419](https://github.com/seancorfield/honeysql/issues/419) by adding `honey.sql.protocols` and `InlineValue` with a `sqlize` function.
   * Address [#413](https://github.com/seancorfield/honeysql/issues/413) by flagging a lack of `WHERE` clause for `DELETE`, `DELETE FROM`, and `UPDATE` when `:checking :basic` (or `:checking :strict`).
 
 * 2.3.911 -- 2022-07-29
diff --git a/doc/extending-honeysql.md b/doc/extending-honeysql.md
index ea4b904..08daf7c 100644
--- a/doc/extending-honeysql.md
+++ b/doc/extending-honeysql.md
@@ -14,6 +14,23 @@ many more. Built in operators include: `:=`, `:+`, `:mod`.
 Built in functions (special syntax) include: `:array`, `:case`,
 `:cast`, `:inline`, `:raw` and many more.
 
+## Extending what `:inline` can do
+
+By default, the `:inline` option can convert a fairly
+basic set of values/types to SQL strings:
+* `nil`
+* strings
+* keywords and symbols
+* vectors
+* UUIDs (Clojure only)
+
+Everything is naively converted by calling `str`.
+
+You can extend `honey.sql.protocols/InlineValue` to
+other types and defining how the `sqlize` function
+should behave. It takes a single argument, the value
+to be inlined (converted to a SQL string).
+
 ## Registering a New Clause Formatter
 
 `honey.sql/register-clause!` accepts a keyword (or a symbol)
diff --git a/doc/options.md b/doc/options.md
index d438aa1..60ff756 100644
--- a/doc/options.md
+++ b/doc/options.md
@@ -83,6 +83,8 @@ was wrapped in `[:inline `..`]`:
 * keywords and symbols become SQL keywords (uppercase, with `-` replaced by a space),
 * everything else is just turned into a string (by calling `str`) and added to the SQL string.
 
+> Note: you can provide additional inline formatting by extending the `InlineValue` protocol from `honey.sql.protocols` to new types.
+
 ## `:params`
 
 The `:params` option provides a mapping from named parameters
diff --git a/src/honey/sql.cljc b/src/honey/sql.cljc
index ea80858..2c819ea 100644
--- a/src/honey/sql.cljc
+++ b/src/honey/sql.cljc
@@ -28,7 +28,8 @@
   * `sql-kw` -- turns a Clojure keyword (or symbol) into SQL code (makes
         it uppercase and replaces - with space). "
   (:refer-clojure :exclude [format])
-  (:require [clojure.string :as str]))
+  (:require [clojure.string :as str]
+            [honey.sql.protocols :as p]))
 
 ;; default formatting for known clauses
 
@@ -263,16 +264,24 @@
       (keyword (name s)))
     s))
 
-(defn- sqlize-value [x]
-  (cond
-    (nil? x)     "NULL"
-    (string? x)  (str \' (str/replace x "'" "''") \')
-    (ident? x)   (sql-kw x)
-    (vector? x)  (str "[" (str/join ", " (map #'sqlize-value x)) "]")
-    ;; issue 385: quoted UUIDs for PostgreSQL/ANSI
-    #?(:clj (instance? java.util.UUID x) :cljs false)
-    (str \' x \') ; UUID cannot contain quotes
-    :else        (str x)))
+(extend-protocol p/InlineValue
+  nil
+  (sqlize [_] "NULL")
+  String
+  (sqlize [x] (str \' (str/replace x "'" "''") \'))
+  #?(:clj clojure.lang.Keyword :cljs Keyword)
+  (sqlize [x] (sql-kw x))
+  #?(:clj clojure.lang.Symbol :cljs Symbol)
+  (sqlize [x] (sql-kw x))
+  #?(:clj clojure.lang.IPersistentVector :cljs PersistentVector)
+  (sqlize [x] (str "[" (str/join ", " (map p/sqlize x)) "]"))
+  #?@(:clj [java.util.UUID
+            ;; issue 385: quoted UUIDs for PostgreSQL/ANSI
+            (sqlize [x] (str \' x \'))])
+  Object
+  (sqlize [x] (str x)))
+
+(defn- sqlize-value [x] (p/sqlize x))
 
 (defn- param-value [k]
   (if (contains? *params* k)
diff --git a/src/honey/sql/protocols.clj b/src/honey/sql/protocols.clj
new file mode 100644
index 0000000..4cf6081
--- /dev/null
+++ b/src/honey/sql/protocols.clj
@@ -0,0 +1,8 @@
+;; copyright (c) 2022 sean corfield, all rights reserved
+
+(ns honey.sql.protocols
+  "InlineValue -- a protocol that defines how to inline
+    values; (sqlize x) produces a SQL string for x.")
+
+(defprotocol InlineValue :extend-via-metadata true
+  (sqlize [this] "Render value inline in a SQL string."))