I will discuss our new results on entanglement and orbital angular momentum (OAM) in non-sequential double ionization (NSDI). We demonstrate that there is entanglement in the OAM between the two photoelectrons in NSDI. Due to the quantization of OAM, this entanglement is easily quantified and has a simple physical interpretation in terms of conservation laws. Using the strong-field approximation, we quantify the entanglement for a large range of parameters, isolating the best targets for experimentalists. We also explore efficient methods to quantify and measure the entanglement, in particular by using an entanglement witness. Importantly, the methodology presented here could be applied to many other systems to help understand and exploit entanglement in attosecond processes.