Wielandt subgroup of a group G is defined to be the intersection of all subnormal subgroups of G. This subgroup was introduced in 1958 by H. Wielandt. GAP provides a programming language and a library of thousands of functions written in GAP language to implement the algorithms on Group Theory. Since 1992, many user contributed programs called Packages have been distributed by GAP. This book is also an effort to contribute to Computational Group Theory as GAP Package. These algorithms helps to compute the various Wielandt subgroups and series of a finite group G, like Wielandt, Generalized Wieladnt, Strong Wielandt, pWielandt, and pStrong Wielandt subgroups and series of a finite group G. T Groups can also be studied with these algorithms.