The focus of experiments and the sophistication of diagnostics employed in Rayleigh Taylor Instability (RTI) induced mixing studies have evolved considerably over the past seven decades. The first theoretical analysis by Taylor and experimental results by Lewis on RTI in 1950 examined two-dimensional, single-mode RTI using conventional photographic techniques. Over the next 70 years, several experimental designs have been used to creating an RTI unstable interface between two materials of different densities. These early experiments though innovative, were arduous to diagnose and provided little information on the internal, turbulent structure and initial conditions of the RT mixing layer. Coupled with the availability of high-fidelity diagnostics, the experiments designed and developed in the last three decades allow detailed measurements of various turbulence statistics that have allowed broadly to validate and verify late-time non-linear models and mix-models for buoyancy-driven flows. Besides, they have provided valuable insights to solve several long-standing disagreements in the field. This review serves as an opportunity to discuss the understanding of the RTI problem and highlight valuable insights gained into the RTI driven mixing process through experiments. For the current review, the focus is on low to high Atwood number (> 0.1) experiments.