Representations of infinite-dimensional algebras and conformal field theory: from $N=2$ to $\widehat{sl}(2\vert1)$

We review a number of constructions, realized in bosonic and $N=2$ strings, whith relate the affine Lie algebra $\widehat{sl}(2)$, affine superalgebra $\widehat {sl}(2|1)$, and the superconformal $N=2$ algebra.