The development and validation of the General Management In-Basket (GMIB) is described. The GMIB is a theory-based generic in-basket simulation, designed to assess supervisory and management skills independent of any job classification. Three of the 15 in-basket items in the GMIB are critical and are scored on a 0-5 scale. The remaining 12 items are scored on a 0-4 scale. Using an item-by-item scoring format, total mean score interrater reliabilities across 4 studies have ranged from 0.86 to 0.95. The GMIB requires only 20 minutes to scores and needs only one rater. In a concurrent validation of the GMIB involving incumbents from 120 job classifications, an estimated true validity of 0.41 was found for predicting the composite of ratings by immediate supervisors on 6 job performance dimensions (n=275). An estimated true validity of 0.44 was found for predicting the composite of ratings by second-level supervisors on the same performance dimensions (n=239). Factor analysis identified four factors for the GMIB, making it possible to retain the dimension format associated with traditional in-baskets. Automated candidate feedback can also be generated with the GMIB. Twelve tables present data from the studies, and an 11-item list of references is included. (SLD)