Overview While theoretical biology is often understood to be primarily mathematical in nature, biology is an inherently historical science with a long tradition of conceptual theorizing, from Charles Darwin to the architects of the Modern Synthesis, and continuing through to today. Biological disciplines ranging from evolutionary biology to ecology, from cell to developmental biology, and from morphology to paleobiology are characterized by a lively interplay among empirical data, mathematical treatments, and conceptual discussions. Like theoretical biology, philosophy of biology is characterized by its attention to conceptual issues. Indeed, over the past several decades, it has evolved to include an increasing number of philosophers with a solid background in science, and whose conceptual interests are often intertwined with those of biologists. Yet, the philosopher brings a distinctive approach and background to the examination of problems in biology; in philosophy, the focus tends to be on the logical structure of theoretical constructs, the uses and interpretation of evidence, the ways in which concepts are employed by scientists, and the relationships between empirical and theoretical elements of research programs. Despite this convergence on conceptual issues, there remains significant and reciprocal distrust between practitioners of biology and philosophy, and too few venues for scholarly interchange and intellectual cross-pollination. This is why P&TB explicitly aims at a mixed audience of philosophers of science and biologists, soliciting papers that are methodologically diverse, including but not limited to standard philosophy of biology analyses of concepts or research programs and 'theoretical' papers by biologists (conceptual, mathematical, and otherwise). Accordingly, we encourage papers submitted for P&TB to be written with the "other" audience in mind. P&TB also publishes select, in-depth reviews pertinent to theoretical biology and philosophy of biology in order to stimulate discussion of recent books and their implications for both biologists and philosophers.