Abstract: We review the progress in studies of spin superconductors over the past few years. A spin superconductor is formed at low temperature by condensed bosons which are electrically neutral but have non-zero spin.We introduce the London-type equations, the Ginzburg-Landautype theory, and the Bardeen-Cooper-Schrieffer-type Hamiltonian, from which various interesting phenomena of spin superconductors are derived, such as zero spin resistance, the electric Meissner effect, and the spin-current Josephson effect. In addition, we examine some systems which may exhibit spin superconductivity, and discuss future possible developments and applications.