Abstract: This invention relates to a convertible step/extension ladder which allows to use one or more of extension sections with a basic A-shaped ladder frame. The extension sections are slidably mounted on legs of the frame through the use of housing/sliding rail arrangement on the legs of the frame and on the extension sections. When converted to an extension ladder, the basic frame portions are folded and locked in that position, while one extension section is moved along the frame portion to rest on the ground. If more than one extension sections are used, the second extension section is mounted on the opposite frame portion and extended upwardly, so that the basic frame portions form a middle part of the ladder.