The quantum Hall effect occurs in two-dimensional electron systems subjected to low temperatures and strong magnetic fields. In this state, the electrical resistance becomes quantized, meaning it takes on discrete values rather than a continuous range. This phenomenon is a result of the behavior of electrons in a magnetic field, leading to the formation of edge states that conduct electricity without dissipation. There are two main types of quantum Hall effects: the integer quantum Hall effect and the fractional quantum Hall effect. The integer effect is characterized by plateaus in the Hall resistance at integer multiples of a fundamental constant, while the fractional effect involves more complex fractional values. Both effects have significant implications for understanding condensed matter physics and have applications in metrology and topological insulators.