This work deals with current fluctuations in mesoscopic conductors. The current fluctuations are investigated in the framework of the full counting statistics, and as an example of experimental relevance we chose the electronic Mach-Zehnder interferometer. A powerful method of introducing decoherence into a coherent conductor is the model of voltage and dephasing probes. We develope a formalism for the full counting statistics of the electronic transport through conductors coupled to voltage and dephasing probes. We compare these models to alternative procedures like phase averaging and find that there is perfect agreement between the models for the case of one probe with a single transport channel. The probe gives additional information on internal properties of the conductor via the fluctuations at the probe. We present the joint counting statistics of current at contacts and voltage at voltage probes coupled to the conductor, as well as the joint counting statistics of current at contacts and occupation number at dephasing probes. In linear transport, the Onsager relations and the fluctuation-dissipation theorem are valid. Beyond the linear regime, there exist fluctuation relations for the full counting statistics which rely on microscopic reversibility away from equilibrium. However, both theory and experiments have shown deviations from micro-reversiblity in the form of magnetic field asymmetric current-voltage relations. We present novel fluctuation relations for non linear transport in the presence of magnetic fields that relate current correlation functions at any order at equilibrium to response coefficients of current cumulants at lower order.