On transfer inequalities in Diophantine approximation

Let $\Theta$ be a point in ${\bf R}^n$. We split the classical Khintchine's Transference Principle into $n-1$ intermediate estimates which connect exponents $\omega_d(\Theta)$ measuring the sharpness of the approximation to $\Theta$ by linear rational varieties of dimension $d$, for $0\le d \le n-1$. We also review old and recent results related to these $n$ exponents.