In this series of articles, we explore how clinical genetics is giving families long-sought answers and transforming autism care. The first story, “Why genetic testing matters for autistic people,” explains some of the factors that limit the availability of genetic tests in the United States. The second story, which we will publish on 13 February, tracks European efforts to reckon with growing demand for genetic tests from parents. As a number of countries scale up the tests they offer, their experiences might offer practical lessons to others. The troves of data they collect could also help scientists link more genetic variants to autism. The third installment in the series, slated to come out in April, will report on the power of family groups — growing numbers of which are coalescing around rare genetic mutations — to drive research.