A pet house comprising: a module formed from a sheet of self-supporting material, comprising: atop panel; a first side panel joined to the top panel along a first fold line; a second side panel joined to the first side panel along a second fold line that is approximately perpendicular to the first fold line; a third side panel joined to the second side panel along a third fold line that is approximately parallel to the second fold line; a fourth side panel joined to the third side panel along a fourth fold line that is approximately parallel to the second fold line; and a bottom panel that is joined to the fourth side panel along a fifth fold line that is approximately parallel to the first fold line; wherein the top panel removably attaches to at least the second side panel, the bottom panel removably attaches to at least the second side panel, and the module may selectively be unfolded into an essentially flat blank or folded to form the module. wherein adjacent panels of the module may be folded adjacent to each other along the fold lines to position the module in a collapsed position; characterized in that the pet house further comprises at least one additional module; and a plurality of clips, wherein any two adjacent modules are attachable to one another by one or more clips passing through a clip corner on one of the modules and an adjacent clip corner on the adjacent module, a plurality of stack alignment tabs on a first module, wherein one or more stack alignment tabs engage with one or more stack alignment channels on a second module when the first module is placed on top of the second module, and wherein one or more door panels, window panels, or transition panels may selectively be removed from each of the modules to enable an animal to pass from an interior space of any module to an interior space of any adjacent module. a module formed from a sheet of self-supporting material, comprising: atop panel; a first side panel joined to the top panel along a first fold line; a second side panel joined to the first side panel along a second fold line that is approximately perpendicular to the first fold line; a third side panel joined to the second side panel along a third fold line that is approximately parallel to the second fold line; a fourth side panel joined to the third side panel along a fourth fold line that is approximately parallel to the second fold line; and a bottom panel that is joined to the fourth side panel along a fifth fold line that is approximately parallel to the first fold line; wherein the top panel removably attaches to at least the second side panel, the bottom panel removably attaches to at least the second side panel, and the module may selectively be unfolded into an essentially flat blank or folded to form the module. comprising: atop panel; a first side panel joined to the top panel along a first fold line; a second side panel joined to the first side panel along a second fold line that is approximately perpendicular to the first fold line; a third side panel joined to the second side panel along a third fold line that is approximately parallel to the second fold line; a fourth side panel joined to the third side panel along a fourth fold line that is approximately parallel to the second fold line; and a bottom panel that is joined to the fourth side panel along a fifth fold line that is approximately parallel to the first fold line; wherein the top panel removably attaches to at least the second side panel, the bottom panel removably attaches to at least the second side panel, and the module may selectively be unfolded into an essentially flat blank or folded to form the module. wherein adjacent panels of the module may be folded adjacent to each other along the fold lines to position the module in a collapsed position; characterized in that the pet house further comprises at least one additional module; and a plurality of clips, wherein any two adjacent modules are attachable to one another by one or more clips passing through a clip corner on one of the modules and an adjacent clip corner on the adjacent module, a plurality of stack alignment tabs on a first module, wherein one or more stack alignment tabs engage with one or more stack alignment channels on a second module when the first module is placed on top of the second module, and wherein one or more door panels, window panels, or transition panels may selectively be removed from each of the modules to enable an animal to pass from an interior space of any module to an interior space of any adjacent module.