Abstract: A shelf, having a pair of brackets which extend downward and then forward from its back edge to engage the back edge and underside of either a step, or the top ledge, of a ladder. A stop member, which may be in the form of a pin loosely slidable in a hole through the shelf is spaced so that when the shelf is engaged on a step and pulled forward to bring the brackets snug against the back edge, the pin drops down to be engagable with the front edge and to prevent the shelf from being inadvertently pushed backward from the step. The pin may be pushed up with one finger under it, and the shelf pushed back to disengage the bracket for removal.