diff --git a/src/calibre/db/cli/cmd_set_custom.py b/src/calibre/db/cli/cmd_set_custom.py
index 2f6f22ae56..819e8d5534 100644
--- a/src/calibre/db/cli/cmd_set_custom.py
+++ b/src/calibre/db/cli/cmd_set_custom.py
@@ -4,19 +4,76 @@
 
 from __future__ import absolute_import, division, print_function, unicode_literals
 
+from calibre import prints
+from calibre.db import _get_series_values
+from calibre.srv.changes import metadata
+
 readonly = False
 version = 0  # change this if you change signature of implementation()
 
 
-def implementation(db, notify_changes, *args):
+def implementation(db, notify_changes, col, book_id, val, append):
     is_remote = notify_changes is not None
-    is_remote
+    field = db.field_metadata.custom_field_prefix + col
+    with db.write_lock:
+        if not db.has_id(book_id):
+            return False, _('No book with id {} exists').format(book_id)
+        try:
+            fm = db.field_metadata[field]
+        except KeyError:
+            return False, _('No column with name {} exists').format(col)
+        if fm['datatype'] == 'series':
+            val, s_index = _get_series_values(val)
+            if s_index is None:
+                s_index = db.get_next_series_num_for(val, field=field)
+            db.set_field(field, {book_id: val}), db.set_field(field + '_index', {book_id: s_index})
+            msg = _('Data set to: {} [{}]').format(db.field_for(field, book_id), db.field_for(field + '_index', book_id))
+        else:
+            if append and fm['is_multiple']:
+                val = list(db.field_for(field, book_id)) + [val]
+            db.set_field(field, {book_id: val})
+            val = db.field_for(field, book_id)
+            if isinstance(val, (tuple, list)):
+                val = fm['is_multiple']['list_to_ui'].join(val)
+            msg = _('Data set to: {}').format(val)
+    if is_remote:
+        notify_changes(metadata((book_id,)))
+    return True, msg
 
 
 def option_parser(get_parser, args):
-    pass
+    parser = get_parser(
+        _(
+            '''\
+%prog set_custom [options] column id value
+
+Set the value of a custom column for the book identified by id.
+You can get a list of ids using the search command.
+You can get a list of custom column names using the custom_columns
+command.
+    '''
+        )
+    )
+
+    parser.add_option(
+        '-a',
+        '--append',
+        default=False,
+        action='store_true',
+        help=_(
+            'If the column stores multiple values, append the specified '
+            'values to the existing ones, instead of replacing them.'
+        )
+    )
+    return parser
 
 
 def main(opts, args, dbctx):
-    raise NotImplementedError('TODO: implement this')
+    if len(args) < 3:
+        raise SystemExit(_('Error: You must specify a field name, id and value'))
+    ok, msg = dbctx.run('set_custom', args[0], int(args[1]), args[2], opts.append)
+    if ok:
+        prints(msg)
+    else:
+        raise SystemExit(msg)
     return 0
diff --git a/src/calibre/db/cli/main.py b/src/calibre/db/cli/main.py
index 40e48619d3..e4634207ce 100644
--- a/src/calibre/db/cli/main.py
+++ b/src/calibre/db/cli/main.py
@@ -21,10 +21,8 @@ from calibre.utils.serialize import MSGPACK_MIME
 COMMANDS = (
     'list', 'add', 'remove', 'add_format', 'remove_format', 'show_metadata',
     'set_metadata', 'export', 'catalog', 'saved_searches', 'add_custom_column',
-    'custom_columns', 'remove_custom_column',
-    # 'set_custom', 'restore_database',
-    # 'check_library', 'list_categories', 'backup_metadata', 'clone', 'embed_metadata',
-    # 'search'
+    'custom_columns', 'remove_custom_column', 'set_custom',
+    # 'restore_database', 'check_library', 'list_categories', 'backup_metadata', 'clone', 'embed_metadata', 'search'
 )