Altermagnets are a newly recognized class of antiferromagnets whose magnetic structure behaves very differently from what is found in conventional systems. In conventional antiferromagnets, the sublattices are linked by simple inversion or translation, resulting in spin-degenerate electronic bands. In altermagnets, however, they are connected by unconventional symmetries such as rotations or screw axes. This shift in symmetry breaks the spin degeneracy, allowing for spin-polarized electron currents even in the absence of net magnetization.