For the general nonlinear Abel integral equation $$\frac{1}{{\Gamma (\alpha )}}\int\limits_0^x {(x - t)^{\alpha - 1} K(x,t,u(t))dt = f(x),{\text{ 0}} \leqslant x \leqslant 1,0 < \alpha < 1,}$$ some theorems on existence and uniqueness of solutions in L P , 1≤p≤∞, and in C[0, 1] are established. Furthermore, methods of regularization are described and stability estimates are given.