With the recent trend toward long-span floors in buildings, there has been an accompanying increase in the incidence of complaints of unacceptable floor vibration after occupancy. This paper details acceptable vibration limits for human tolerance. In addition, the magnitudes and time durations of motions of floors of different constructions resulting from foot-falls (persons walking) are examined.The relative floor vibrational behavior resulting from variables such as unsupported span, type of structure (open web joist-concrete deck or reinforced concrete, etc.) composite or noncomposite deck-structure, etc., is discussed. The relative effect of each variable is outlined and ranked. Guidance on the relationship of variables is provided for the designer of long-span floors. Approaches to ‘correcting’ floors exhibiting an unacceptable floor vibrational behavior are discussed. Case histories of floors that have been modified to improve vibrational response are also given.