Over the last 20 years, the development of a wide range of treebanks that track the evolution of languages’ syntactic patterns through time has revolutionized the field of historical syntax. The range of treebanks now available facilitates research into the long histories of many of the major Indo-European languages. Although the field's essentially corpus-based methodology has not changed, the quantity of data now available and the ease and precision with which those data can be extracted have created new opportunities. For example, with a treebank it is possible to extract all examples of surface strings associated only with abstract structures (e.g., relative clauses, extraposition), to investigate predictions made by syntactic analyses, to search for rare constructions, and to extract enough data to support sophisticated statistical analyses. Crucially, treebanks make verification and replicability of results possible.