If Earth lost its magnetic field, would its ability to support life be diminished? If Mars had retained a strong magnetic field, would it be habitable today? For decades it was assumed that the answers to these two questions were "yes". In recent years, however, the canonical assumption that planetary magnetic fields improve planetary habitability has been called into question. This presentation will review the perceived connections between magnetic fields and surface and atmospheric habitability of planets and discuss several approaches to resolving this important question: (1) intercomparison of observations of Venus, Earth, and Mars, (2) analysis of observations from unmagnetized and magnetized regions of Mars, and (3) development of large computer simulations for the interaction of a star with a planet?s atmosphere and magnetic field. In the end, all approaches are likely to be necessary. We will discuss an ongoing team science effort named MACH that draws on expertise from the heliophysics, planetary, and exoplanetary communities. Prof. Brain is hosted by Dr. Karan Molaverdikhani (karan@lsw.uni-heidelberg.de).