The talk of Tamir Bendory will focus on invariants for the multireference alignment (MRA) and cryo-EM problems. MRA is a simplification and abstraction of the cryo-EM problem. In MRA, we aim to estimate a signal from its circularly-translated copies in high noise regimes. It will be shown that the optimal estimation rate for MRA can be achieved by exploiting features of the signal that are invariant under translation. In a similar manner, these invariant features are used for the heterogeneous MRA problem in which one aims to estimate multiple signals simultaneously. Then, the invariants of the cryo-EM problem will be discussed using the framework of Kam's method. We will show how an ab initio model of the molecule can be estimated directly from the data, without estimating the viewing direction. Finally, we will discuss extensions of Kam's method.