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Interplanetary dust particles (IDPs) are from asteroids and comets, and they are the smallest and most fine-grained meteoritic objects available for laboratory investigation. Cometary IDPs are of special significance because they are presently the only samples of comets, and comets are expected to be enriched in preserved solar nebula and presolar components. These components may include not only cosmically rare refractory circumstellar grains(e.g. SiC) that are recovered from meteorites but also cosmically abundant interstellar silicates and carbonaceous grains that were the fundamental building blocks of the Solar System. D/H ratios measured in IDPs are consistent with the survival of interstellar carbonaceous material, and some IDPs contain glassy grains with properties similar to those of interstellar “amorphous silicates”. Submicrometer forsterite and enstatite crystals in IDPs resemble circumstellar silicates detected by the Infrared Space Observatory (ISO). ISO also detected a broad ~ 23 µm feature around several stars, and a similar feature observed in IDP spectra is due to submicrometer FeNi sulfide grains, suggesting that sulfide grains may be a significant constituent of astronomical dust.