Meta-analyses of over 100 studies show brain size correlates 0.24-0.40 with IQ. Brain size 1 SD above average predicts IQ 0.24-0.40 SD above average. MRI-measured brain volume correlates 0.38 with IQ versus 0.20 for external measures. Brain size predicts IQ better in healthy people (0.26) than clinical samples (0.21). IQ subtests correlating with brain size also correlate 0.63 with general intelligence g. Genetic correlation exists between IQ and brain size from shared genes. Longitudinal studies show brain size changes predict IQ changes. Brain size and IQ both peak in mid-20s and decline in old age. Breeding mice for maze-solving intelligence over 12 generations produces brains 2.5 SD larger. Worldwide IQ rise parallels brain size increase. Human evolution shows larger brains with rising intelligence across species. Within-family studies confirm larger-brain siblings have higher IQ. Four of five family studies find brain size predicts sibling IQ differences. Men have larger brains than women but equal or higher male IQ due to neuron density or other factors. Megalencephaly cases irrelevant as they involve pathological brains. Nisbett dishonestly cherry-picked one null family study ignoring four positive ones.