  In this paper Arnold diffusion is proved to be a generic phenomenon in nearly
integrable convex Hamiltonian systems with arbitrarily many degrees of freedom:
$$ H(x,y)=h(y)+\eps P(x,y), \qquad x\in\mathbb{T}^n,\ y\in\mathbb{R}^n,\quad
n\geq 3. $$ Under typical perturbation $\eps P$, the system admits "connecting"
orbit that passes through any finitely many prescribed small balls in the same
energy level $H^{-1}(E)$ provided $E>\min h$.
