For over a decade the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has been using the most sensitive radio telescopes in the world--the Green Bank Telescope and Arecibo--to monitor millisecond pulsars. The goal of the NANOGrav is to directly detect low-frequency (nano-Hertz) gravitational waves, which cause small correlated changes in the times of arrival of radio pulses from millisecond pulsars. The most promising sources of gravitational waves at these frequencies are supermassive binary black holes that coalesce following the mergers of galaxies. In this talk I will discuss the work of NANOGrav, our sensitivity to gravitational waves including detection and astrophysical prospects for the next few years, as well as plans for low-frequency gravitational-wave astrophysics and instrumentation in the next decade and beyond.