The weak interaction is mediated by three vector bosons. These differ form the other exchange particles in several ways. All three have mass and two of them (W⁺ and W^-) are electrically charged.

The weak force also has a different characteristic compared to the other three forces. It can hardly be understood as a force in the traditional sense. Instead it is responsible for many types of particle transformations. It can transform one quark into another and thereby transform for example a neutron in an atomic nucleus into a proton. An electron and an electron-neutrino are emitted in this process - we say that the atomic nucleus is decaying. It is important to understand that it is a quark in the neutron that is transformed into an other quark (d->u) and that at the same time an electron and a neutrino are created - they did not exist inside the nucleus from the beginning!

The weak interaction is also the reason that charged leptons as e.g. the muon, decays into a lighter lepton (electron or positron). The weak interaction has three exchange particles: W⁺, W^- and Z⁰. But in each transformation it is only one of these that is involved.