This paper reports the experimental results of the fast pyroysis of wood sawdust performed in two different cyclone reactors. The mass balances are close to 100% and the char fractions always smaller than 3%. The flexibility of the cyclone reactor is such that, according to the operating conditions, it can be used either for the fast gasification or for the fast liquefaction of biomass. Side experiments reveal that a fraction of the gaseous products can be used as the carrier gas (recycling process) without noticeable changes of the gas composition and with fast gasification yields close to 100%. It is shown that the Vapor-phase cracking reactions mainly occur inside a very thin and hot boundary layer close to the heated surface of the cyclone. The results of the modeling of these phenomena are used to derive kinetic constants that prove to be in very good agreement with those of the literature. The conclusion is that the cyclone appears as a very efficient multifunctional reactor making it possible to perform in less than a second heating and pyrolysis of the reactants as well as the quenching and separation of the products.