Direct observations have established the size distribution of interplanetary meteoroids at 1 AU as well as the dependence of the spatial density with respect to the distance from the sun. After evaluating the consequences of mutual collisions and the effect of radiation pressure the following conclusions can be drawn: 1. Catastrophic collisions dominate the lifetimes of meteoroids with masses m ≳ 10−5g. About 10 tons per second are lost within 1 AU (mostly in form of 10−4g to 10−1g particles). Under steady state conditions these meteor sized particles have to be replenished by other sources, e.g. comets. 2. After being crushed by collisions 70 to 85% of this mass will be in form of particles with masses 10−10g ≲ m ≲ 10−5g. Part of these “zodiacal light” particles (about 0.3 tons per second) are transported by the Poynting Robertson effect towards the sun where they will evaporate. However, since the collisional production of these intermediate sized particles exceeds their losses this population is presently not in equilibrium. 3. 15 to 30% of the collisional fragments have masses m ≲ 10−10 g. Most of these small particles will be injected into hyperbolic orbits by radiation pressure (β-meteoroids).