In this paper, we provide a direct approach to K-reflections of T 0 spaces. For a full subcategory K of the category of all T 0 spaces and a T 0 space X, let K(X) = {A ⊆ X : A is closed and for any continuousWe call K an adequate category if for any T 0 space X, P H (K(X)) is a K-space. Therefore, if K is adequate, then K is reflective in Top 0 . It is shown that the category of all sober spaces, that of all d-spaces, that of all well-filtered spaces and the Keimel and Lawson's category are all adequate, and hence are all reflective in Top 0 . Some major properties of K-spaces and K-reflections of T 0 spaces are investigated. In particular, it is proved that if K is adequate, then the K-reflection preserves finite products of T 0 spaces. Our study also leads to a number of problems, whose answering will deepen our understanding of the related spaces and their categorical structures.