Abstract: We introduce fiber sequences and the Hopf fibration $S^3 \to S^2$ in HoTT, and we show that the Hopf fibration induces equivalences between the homotopy groups $\pi_k$ of $S^3$ and $S^2$ for $k>2$. We also deduce that $\pi_2(S^2)$ is equivalent to $Z$. We will review the background on truncations and connectedness in this talk too.