This Perspective reviews our recent efforts towards the low-temperature synthesis of complex perovskite oxide ABO₃ (A = Sr, Ba; B = Ti, Zr) nanocrystals using the vapor diffusion sol–gel method and the determination of their room-temperature crystal structure. From a synthetic standpoint, emphasis is placed on demonstrating the ability of the vapor diffusion sol–gel approach to yield compositionally complex nanocrystals at low temperatures and atmospheric pressure without the need for postsynthetic heat treatment to achieve a crystalline and phase-pure oxide product. The ability to successfully achieve this is illustrated using Ba_1−xSr_xTi_1−yZr_yO₃ (0 ≤ x ≤ 1, 0 ≤ y ≤ 1) and Eu³⁺-doped Ba(Ti,Zr)O₃ nanocrystals as examples. From the standpoint of the structural analysis, emphasis is placed on highlighting how multiple and complementary spectroscopic techniques that probe atomic correlations in short (≤1 nm), intermediate (∼1–3 nm), and long (≥3 nm) length scales can be employed to gain insight into the atomic structure of the resulting nanocrystals. Examples that clearly illustrate this strategy of structural characterization are the investigation of the size- and composition-dependence of the structure of polar nanoregions in sub-10 nm BaTiO₃ and sub-20 nm Ba_1−xSr_xTiO₃ and BaTi_1−yZr_yO₃ nanocrystals, and the investigation of the distribution of rare earth dopants in sub-15 nm Eu³⁺:BaTiO₃ nanocrystals.