Psychometric, cognitive, and educational researchers have produced seemingly conflicting results about the nature, modifiability, and heritability of intelligence. In this introduction, the key tenets and evidence for their respective positions are reviewed, and the historical context for these positions is described. The following concepts are emphasized: singularity versus modularity, heritability, interactive nature of genes, and context. The role of both environmental and biological determinants of intelligence is supported, and some evidence is presented that is incompatible with extreme views of causation.