Summary: The article, being a continuation of the first one [ibid. 78, 153--192 (2001; Zbl 1031.34002
)], deals with the so-called differential equations of fractional order in which an unknown function is contained under the operation of a derivative of fractional order. The methods and the results in the theory of such fractional differential equations are presented including the Dirichlet-type problem for ordinary fractional differential equations, studying such equations in spaces of generalized functions, partial fractional differential equations and more general abstract equations, and a treatment of numerical methods for ordinary and partial fractional differential equations. Problems and new trends of research are discussed.