The exact formation mechanism of many heavy elements remains unknown. Models of the formation site and environment have greatly improved over the past decades, and experiments have provided new data for many of the heavy isotopes. However, much information is still missing to fully describe the neutron-capture formation processes and their sites. Stellar observations combined with mass spectroscopy of meteorites can help to place some of the needed constraints. This, in turn, will help to improve the models and our knowledge on the formation channels creating these heavy elements. Recent studies of Mo, Ru, Pd, and Ag showed that different processes or environments other than the main r-process (forming, e.g., Eu) are needed to explain the production (and observations) of elements with 40 < Z < 50. An observational study of Mo-Ag is presented, where stellar abundances are compared to meteoritic isotopic abundances (at metallicities [Fe/H] > -1.5) to extract information on differences or similarities in their production. Finally, the number of formation processes needed to describe the chemical composition in low metallicity stars ([Fe/H] < -2.5) is discussed.