We offer many different kinds of grants: training grants, fellowships, career development awards, scientific meeting grants, awards for small businesses, centers, and even construction awards (elsewhere at NIH).
To distinguish between these different kinds of grants, we name these programs differently and code them with different strings of letters and numbers. The letter-number strings are called "activity codes." Dr. Robin Barr, director of the NIA Division of Extramural Activities, has a new blog post describing activity codes for research grants. "An R01 research project grant is the dollar bill of NIH," Dr. Barr writes. "It is our most recognized award, our most common award, our most flexible award, and our most understood award. So why is it not our only award?"
Read the full blog post: Activity codes—why not R01 and only R01? 
The NIA blog publishes weekly with information on grants and funding policy, research priorities, scientific meetings, and topics of interest to researchers and others in the scientific community. Subscribe  to get it weekly in your email inbox, or grab the RSS feed .