The majority of the interplanetary dust particles (IDPs) collected in the stratosphere belong to one of three major classes, the first two dominated by the anhydrous minerals olivine and pyroxene, and the third by hydrous layer-lattice silicates. Infrared spectroscopy and transmission electron microscopy studies show that the different IDP classes represent different types of dust that exist as individual particles in interplanetary space. The majority of the collected IDPs smaller than 30 micrometers in diameter in the layer-lattice silicate and pyroxene classes appear not to have been heated to temperatures above 600 degrees C during atmospheric entry. The relatively low maximum temperatures experienced by these IDPs during atmospheric entry imply that they arrive at the top of the atmosphere with low geocentric encounter velocities. This limits the possible encounter trajectories for these particles to relatively circular, prograde orbits. As a result, it is unlikely that these IDPs are from Earth-crossing comets or asteroids. Asteroids, and comets having low inclinations and perihelia outside 1.2 AU, appear to be the best candidates for the parent bodies of the pyroxene and layer-lattice silicate particles. Chemical and mineralogical information suggests that the pyroxene-rich IDPs are from comets and the layer-lattice silicate-rich IDPs are from asteroids. The collected IDPs dominated by olivine appear to include a larger fraction of particles heating above 600 degrees C, suggesting that these particles were captured from more eccentric orbits. This, and the observation of the infrared spectral features of olivine in several comets suggest these particles have a cometary origin. Since much of the collected dust has apparently been captured from nearly circular, prograde orbits and since there are no appropriate parent bodies presently in such orbits, these results provide an experimental confirmation that the Poynting-Robertson effect exists as a nongravitational force important in the orbital evolution of dust in the Solar System.