Theory and evidence converge to suggest perfectionism is a personality construct that matters a great deal and is linked with many consequential outcomes (e.g., depression, eating disorders, suicide, marital problems, and procrastination). With the multidimensional perfectionism construct turning 30 years of age, our review critically examines the past and the future of this construct with a focus on the six landmark dimensions of Hewitt and Flett’s (1991) and Frost et al.’s (1990) seminal models: Self-oriented perfectionism, other-oriented perfectionism, socially prescribed perfectionism, personal standards, concerns over mistakes, and doubts about actions. Our review considers both what we understand about these dimensions given the extant empirical literature (i.e., known knowns) and areas where gaps exist in our understanding of multidimensional perfectionism and its consequences (i.e., known unknowns). Evidence suggests the core dimensions of Hewitt and Flett’s (1991) and Frost et al.’s (1990) trait and attitudinal models of perfectionism, respectively, are neither captured by nor redundant with other well-established predictors. In fact, these perfectionism dimensions appear to represent core vulnerability factors that are tied intimately to the development and maintenance of a wide range of maladaptive outcomes.