Bloomfield’s earliest work was in historical Germanic studies, beginning with his dissertation, and continuing with a number of papers on Indo-European and Germanic phonology and morphology.
His post-doctoral studies in Germany further strengthened his expertise in the Neogrammarian tradition, which still dominated Indo-European historical studies. Bloomfield throughout his career, but particularly during his early career, emphasized the Neogrammarian principle of regular sound change as a foundational concept in historical linguistics