We studied morphological, physical, chemical and mineralogical properties of six Costa Rican Andepts to elucidate the problems of classification, productivity, and management of ash-derived soils. The soils were formed on volcanic ash, predominantly andesitic, during Pleistocene and recent times. These ash-derived soils are found at elevations higher than 600 m, with model profiles occurring at elevations between 1000 and 1800 m. The climate is cool (15 to 22°C, mean annual temperature) and humid (1170 to 3534 mm, mean annual rainfall), and the original vegetation was a humid forest. These Andepts have a fairly uniform morphology, and the amorphous materials have become strongly stabilized with the soil organic matter to give the dark color, loamy texture, granular-fluffy structure, friable-smeary (thixotropic) consistence, acid reaction, good internal drainage, low bulk density, high porosity and water retention, and high cation exchange capacity that are unique and diagnostic in Andepts. One soil is a Hydric Dystrandept and five are Typic Dystrandepts.