It is now widely recognized that retrotransposons 
such as Long Interspersed Element-1 (LINE1 or L1s) have 
played an instrumental role in shaping the structure and 
function of our genomes. L1s contribute to ~17% of total 
human genome, and there is increasing evidence of its 
active role in neuronal development. L1s retrotransposition 
was proposed as a potential mechanism of generating 
neuronal genome diversity, and multiple groups have 
attempted to characterize L1s retrotransposition events and 
their impacts on brain function and physiology. L1s are 
also linked to cognitive and psychiatric diseases such as 
Rett syndrome and schizophrenia. Here, I discuss the recent 
progress in characterizing the L1s retrotransposition in 
neuronal development, and how the knowledge has 
contributed to our understanding of brain function and 
diseases.