Chimeras, individuals whose genetically distinct cell lines originated from different zygotes, are attracting attention among twin researchers. This is because chimerism may occur more frequently than previously suspected, having been observed among 8% of dizygotic (DZ) twins and 21% of DZ triplets. The presence of separate cell lines in these twins may hold clues to disease susceptibility, developmental complications and histocompatibility features. Next, new twin research on physical development is offering fresh insights on height and hormones, height and education, and pelvic development. Finally, twins having twins, twins deserting the military and twins composing music raise new thoughts about reproduction, behavior and talent.