In this overview talk I will introduce main concepts and results of quantum estimation theory, including the symmetric logarithmic derivative and the quantum Fisher information. I will talk about its relation to information geometry and quantum speed limits. I will discuss how the theory relates to the description of quantum sensors and I will discuss relation to fidelity susceptibility, which is often used to describe phase transitions and critical phenomena in many-body systems.  I will introduce some computation methods for the figures of merit and discuss this theory in the wider framework of quantum tomography methods.