Halogens are strong oxidizing agents as they have strong tendency to accept electrons. The oxidizing strength decreases from fluorine to iodine.
Due to low bond dissociation enthalpy, high electronegativity and large electron gain enthalpy, halogens have strong tendency to accept electrons and thus get reduced.
X+e−→X−
In other words, halogens act as strong oxidising agents, their oxidising power, however, decreases from F2 to I2 as is evident from their electrode potentials: