His work emphasized a phenomenological and subjective approach to therapy, noting that many of us split off our experience (thoughts, sensations, emotions) that are uncomfortable. One goal of his work is to move people into owning their experience and developing into a healthy gestalt (or whole). Perl's book Gestalt therapy verbatim is an interesting description of this approach drawn from transcripts of his work.
Gestalt therapy was originated about fifty years ago by Frederick 'Fritz' Perls (1893-1970) in collaboration with Paul Goodman.