Confirmation bias is regarded as an important phenomenon of human cognition, but a clear characterization is not a simple matter. Following earlier analyses, we distinguish two components of confirmation bias as concerning the search for new evidence vs. the assessment of given evidence, respectively. We describe classic findings and discuss their implications. An array of ensuing issues are addressed: the difference and connection between the logical concept of confirmation and human reasoning, what normative constraints are relevant to detect confirmation bias, whether the evidence indicating confirmation bias is ultimately compelling, how the notion relates to other cognitive phenomena of interest, and how one can make sense of such an apparently defective trait in an evolutionary perspective.