We have made many advances in our understanding of interstellar dust. However, many details about its origin and evolution are still unclear. Major unresolved issues are the efficiency of dust formation in the various sources, especially supernovae; the composition and the in-situ survival of the newly-formed dust; the efficiency of grain destruction in the ISM; the reconstitution of dust particles by accretion in molecular clouds and the resulting dust composition; and finally, the global effects of dust evolution on galactic opacities and the redistribution of stellar energies into infrared emission.
Currently operating and future space-, air-, and ground-based observatories will provide a wealth of new information which will go a long way towards addressing and solving many of the issues raised above.
Acknowledgments
I thank Richard Tuffs and Cristina Popescu for organizing a scientifically stimulating conference in a beautiful surrounding, and Rick Arendt for suggesting a more accurate form for eq. (7) than appeared in the original version of the manuscript, and for comments that greatly enhanced the clarity of this paper. This work has been supported by the NASA OSS Long Term Space Astrophysics Program LTSA-2003-0065.