The impact of La, Zr and Hf content on the crystal phases and ferroelectric and dielectric properties of (Hf,Zr,La)O2 has been determined by investigating epitaxial films. The polarization of La-doped Hf1-xZrxO2 films strongly depends on La and Zr content, with remanent polarization ranging from 0 to about 30 µC/cm2. The optimal La doping in Hf1-xZrxO2 increases from 0% to 2–5% for decreasing the Zr content from 100% (ZrO2) to 0% (HfO2). Structural characterization and dielectric permittivity measurements point to the correlation between crystal phases and polarization. In ZrO2 films, an orthorhombic/tetragonal phase mixture likely evolves into a monoclinic/cubic/tetragonal phase mixture as La doping increases. In films with Hf content, when La content increases, the phases present in Hf0.5Zr0.5O2 progressively evolve from orthorhombic and monoclinic to cubic, and in HfO2 from monoclinic, to orthorhombic, and finally to cubic. This map of phases and polarization in the Hf-Zr-La oxide, established with epitaxial films, can be a model system for polycrystalline samples. Financial support from the Spanish Ministry of Science and Innovation (MCIN/AEI/ 10.13039/501100011033), through the Severo Ochoa FUNFUTURE (CEX2019-000917-S), PID2020-112548RB-I00 and PID2019-107727RB-I00 projects, and from CSIC through the i-LINK (LINKA20338) program is acknowledged. We also acknowledge project TED2021-130453B-C21, funded by MCIN/AEI/10.13039/501100011033 and European Union NextGenerationEU/PRTR. TS is financially supported by China Scholarship Council (CSC) with No. 201807000104. TS work has been done as a part of his Ph.D. program in Materials Science at Universitat Autònoma de Barcelona. With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S). Peer reviewed