Whilst person-centered and experiential approaches to counseling and psychotherapy are often dismissed as empirically unsupported treatments, many clinical practitioners have only a limited awareness of the most recent empirical findings regarding these ways of working. Drawing on meta-analyses and summaries of meta-analytical data from leading international psychotherapy researchers -- such as Mike Lambert, Louis Castonguay, and Robert Elliott -- this paper will present a state-of-the-art, critical review of the evidence-base for person-centered and experiential therapies. It will begin by presenting the latest meta-analytical findings on person-centered and experiential approaches, and then go on to review relevant process-outcome research, with a particular emphasis on the role of client motivation and agency in effective therapeutic outcomes, and the centrality of the therapeutic relationship. The paper will conclude that person-centered and experiential approaches to therapy have a much stronger evidence base than they are often given credit for, and that a number of process-outcome findings in the counselling and psychotherapy field point towards their effectiveness and efficacy.