This article offers a brief overview of historical linguistics and explores the value of historical "sign" linguistics. The specific focus of the article is on the question of the extent to which the concept of "sign language families" is a legitimate and useful one. It is suggested that although lateral transmission and interference may account for a great deal of the similarity between and among sign languages, descent from a common linguistic ancestor (as in the cases of American Sign Language and French Sign Language) can also often be documented. It is observed that sign languages seem to change at a much more rapid rate than do spoken languages, but this is suggested to have at least as much to do with factors such as the intragenerational transmission of most sign languages as any other variable. Finally, it is argued that regardless of its status in historical linguistics more generally, lexicostatistics has consistently been demonstrated to be a powerful methodological tool in understanding the relationships between and among different sign languages.