  We investigate several phenomenological implications of the Weak Gravity
Conjecture (WGC). We find that the WGC implies that the SM neutrinos must be
electrically neutral, that the electric charge in the SM must be quantized, and
that the photon must be massless. In addition, we use the WGC to set lower
bounds on the electric charge of milli-charged particles (mCP), the gauge
coupling of several $U(1)$ extensions of the SM, their kinetic mixing parameter
with the SM $U(1)_{\text{EM}}$, and the axion couplings to photons and
fermions. We also set an upper bound on the lifetime of the proton.
