In this chapter, we will talk about various types of errors in quantum computers, including initialization errors, readout errors, gate errors, bit-flip errors, and phase errors. To understand errors, the quantum master equations need to be used. However, this is beyond the scope of this book and will not be covered. Then we will discuss two of the most common methods to measure the decoherence times of a qubit, namely the \(T_1\) and \(T_2\) times. We will use superconducting qubits as examples to demonstrate the steps and understand the results.