A pet step is a modular foam core item which can be used alone or in an arrangement with other pet steps—referred to as cubes—to form a stair and offers a comfortable way for a pet that has been debilitated by age, surgery, illness, or injury to climb, e.g., from the floor to the couch and down, eliminating the impact of jumping. Each step is formed of a washable fabric cover stretched across a high-density foam core, the core being usually of regular block shape, but alternatively in the shape of a trapezoidal block, right wedge, or other. The cover may be made from various fabrics with different textures, colors, and designs, and is secured around the foam core using a band of elastic. Thus, the cover is easily removable and washable. The pet steps are intended to be used in a stair, formed by placing the steps adjacent one another with the elasticized opening of the cover on the bottom sides of the steps and mating and engaging the optional fasteners, such as hook-and-loop fasteners, which are mounted between the adjacent step surfaces.