The Rescue of Janet van Dyne was a planned extraction of Janet van Dyne from the Quantum Realm by Hank Pym.
During a mission for S.H.I.E.L.D. with her husband Hank Pym, Janet van Dyne, operating as the Wasp, used the capabilities of her Wasp Suit to shrink to an atomic level in order to stop a missile. Although she successfully destroyed the rocket, this caused her to fall into the Quantum Realm, where she was trapped for decades.
Both Pym and their daughter Hope van Dyne thought that Janet was dead. However, when Scott Lang was in turn trapped in the Quantum Realm but managed to return, Pym began hoping that Janet was still alive and that he could rescue her.
Two years later, following the Clash of the Avengers, Lang (while on house arrest) received an apparent message from Janet in the form a shared memory of her daughter Hope, which allowed Pym and Hope to confirm their suspicions about Janet being still alive. They briefly opened a tunnel to the Quantum Realm, however, it was only able to be open for a few seconds.
Later, when able to open a more stable tunnel, Janet, sending a message through Lang, gave her exact location, before revealing that there were only two hours before the Quantum Realm's instability would move her, causing her to disappear for another century.