Systems and apparatus related to footwear including a modular lacing engine are discussed. In an example, a modular footwear apparatus including an upper portion, a lower portion, and a lacing engine is described. The upper portion can include a lace to adjust fit of the upper portion against a foot, the lace adjustable between a first position and a second position based at least in part on manipulation of an effective length of the lace. The lower portion can include a mid-sole and an out-sole, and the lower portion can be coupled to the upper portion at the mid-sole. The lacing engine can include a top-loading lace spool to engage a loop of the lace to enable manipulation of the effective length of the lace through rotation of the lace spool, the lacing engine received within a cavity in the lower portion.