  Stellar nucleosynthesis is the corner-stone of many astrophysical problems.
Its understanding, which can be tested by countless observations, leads to
insights into the stellar structure and evolution, and provides crucial clues
to the physics of the galaxies and of the universe. Precise answers can be
given to the questions ``When, where and how the chemical elements are
synthesized in stars?", and will be summarized in this paper for what concerns
stars of low and intermediate mass. However, in spite of the observational
confirmation of many predictions, important and complementary data reveal some
weaknesses in the theory of stellar physics. In particular, the mixing
processes of chemicals inside the stars, as well as the mass loss and ejection
mechanisms, are poorly known. Their rudimentary treatment imposes the use of
parameters which strongly influence the predicted chemical yields. In our
discussion, we will underline the future developments that may lead to
quantitative changes in the predictions of chemicals production by low and
intermediate mass stars.
