The modular moving carts include removable, attachable shelf storage units which are useful in two, three or four different positions. By changing the relative positions of the units, i.e., standing and facing one direction, they form bookcases/storage areas having a depth to accommodate books, or to form deep shelves to accommodate computers, typewriters, etc., and in a position lying down, to form a container or bin. The cart includes a rectangular base member having four outer edges adapted to support and retain two or more shelf storage units and has a predetermined width, a predetermined length and a predetermined area (based on the width multiplied by the length), with a plurality of wheels attached thereto. There is also at least one first type of shelf storage unit and at least one second type of shelf storage unit included in the present invention. The first shelf storage unit has a top, a bottom, and two opposing vertical side walls situated perpendicularly to the top and bottom, and an open front and an open back. The first shelf storage unit is removably attachable to the rectangular base member. The second shelf storage unit has a top, a bottom, two opposing vertical side walls, a back wall and an open front, and is removably attachable to the rectangular base member. The second shelf storage unit has a first vertical placement position and a second vertical placement position, and at least one horizontal placement position.