Yeates, A. R., & Berger, M. A. (2024). Introduction to Field Line Helicity. In K. Kuzanyan, N. Yokoi, M. K. Georgoulis, & R. Stepanov (Eds.), Helicities in Geophysics, Astrophysics and Beyond (3-16). Hoboken, NJ, USA: American Geophysical Union. https://doi.org/10.1002/9781119841715.ch1