Depleted Monolithic Active Pixel Sensors (DMAPS), also known as depleted CMOS sensors, are extremely attractive for particle physics experiments. As the sensing diode and readout electronics can be integrated on the same silicon substrate, DMAPS remove the need for hybridization. This results in thin detectors with reduced production time and costs. To achieve high speed and high radiation tolerance, DMAPS are manufactured in High Voltage (HV) processes on High Resistivity (HR) wafers. Today’s most performant DMAPS are 50 µm thin and have 50 µm x 50 µm cell size with integrated mixed analog and digital readout electronics, 11 ns time resolution and 5 x 1015 1 MeV neq/cm2 radiation tolerance. DMAPS in HR/HV-CMOS have been adopted as the sensor technology for the pixel tracker for the Mu3e experiment and are under consideration for the ATLAS detector Phase-II Upgrade. However, in spite of the major improvements demonstrated by DMAPS, further research to achieve even more performant sensors is needed to realize the full potential of these sensors to meet the most challenging requirements for particle physics experiments planned for the future. This article describes the state-of-the-art of DMAPS in terms of time resolution and radiation tolerance, and presents specific work done by the CERN-RD50 collaboration to further develop the performance of these sensors.