The basic mechanism by which dust particles are charged through impact was studied. Redistribution of charges during impact was described in terms of the dynamics of the impacting bodies, and the properties of the materials of the contacting surfaces. An electrostatic probe theory was developed and applied to three cases: single particles, clouds of particles, and turbulent suspensions. Experiments were performed with pulverized coal dust suspended in air, a principal area of application of the electrostatic probes utilizing impact charging. Results showed that the electrostatic probe provides an accurate means for monitoring the flow rate of particles in a dusty suspension.