  We study the homotopy category $\mathsf{K}_{N}(\mathcal{B})$ of $N$-complexes
of an additive category $\mathcal{B}$ and the derived category
$\mathsf{D}_{N}(\mathcal{A})$ of an abelian category $\mathcal{A}$. First we
show that both $\mathsf{K}_N(\mathcal{B})$ and $\mathsf{D}_N(\mathcal{A})$ have
natural structures of triangulated categories. Then we establish a theory of
projective (resp., injective) resolutions and derived functors. Finally, under
some conditions of an abelian category $\mathcal{A}$, we show that
$\mathsf{D}_{N}(\mathcal{A})$ is triangle equivalent to the ordinary derived
category $\mathsf{D}(\mathsf{Morph}_{N-2}(\mathcal{A}))$ where
$\mathsf{Morph}_{N-2}(\mathcal{A})$ is the category of sequential $N-2$
morphisms of $\mathcal{A}$.
