This chapter focuses on recent advances on the synthesis, structure, characterization and chemical reactivity of alkenes, alken(yn)yl and allyl-based group 3 and lanthanide organometallic complexes. The synthetic methods to access to such compounds are presented in detail, followed when particularly relevant by some typical structural data issued from usual characterization methods in solution and in the solid state, such as NMR spectroscopy and X-ray diffraction studies. The chemical properties of the complexes are briefly described, including stoichiometric as well as catalytic reactions. Theoretical studies in support of experimental results are also presented in this chapter.