The self consistency conditions for magnetic turbulence are reviewed. The principal features of a magnetic topology involving stochastic flux lines-transport, ambipolarity, basic equations-are summarized. Two driving sources are considered: thermal effects which require large scale residual islands and electron diamagnetism which involves fluctuation scales smaller than the ion Larmor radius and a poloidal beta threshold of order one. Detailed stability criteria and transport coefficients are given in each case.