As the atomic layer deposition (ALD) method is based on sequential, self-limiting surface reactions the precursor chemistry is the key to a successful processing of conformal high quality thin films. ALD precursor chemistry has traditionally been based on homoleptic compounds such as, but not limited to, metal halides, alkylamides and alkoxides. However, these precursors sometimes have drawbacks such as possible halide contamination and low thermal stabilities. Consequently, heteroleptic precursors have been investigated as alternatives to the existing homoleptic counterparts, leading to the development of several advantageous processes. Here, examples of heteroleptic precursors for ALD processes of transition metals and their oxides are given. Special focus is given to oxides of the rare earths and groups 4 and 5. Trends in the properties of heteroleptic precursors are discussed. Several examples of our recent results are shown, including introduction of novel processes based on amidinate-cyclopentadienyl complexes for ALD of rare earth oxides.