In seasons three and four, Meredith and Derek 's relationship becomes rocky and they each take time to date other people. Derek 's plans to propose were ruined by a series of unfortunate events in season five. In the season finale, they decide to give their planned wedding to Alex and Izzie. Due to their tight schedule, they instead informally marry and Derek writes down their "promises '' on a post-it note. They legalize their marriage in season seven in order to adopt Zola, a young African orphan treated for spina bifida. They briefly separate after Meredith tampers with their Alzheimer 's trial, jeopardizing her career and tarnishing Derek 's reputation. Zola is taken away from Meredith after a social worker finds out she and Derek are living separately. In later seasons, Derek often griped about how his subsequent interns and residents -- mainly Lexie Grey, Shane Ross and Heather Brooks -- did not quite measure up to Meredith. The social worker comes back and announces they are the official parents of Zola. As Meredith nears the end of her fifth year of residency, she and Derek are torn between staying at Seattle Grace Mercy West or leaving for Boston where Derek would work at Harvard while Meredith would be at the Brigham and Women 's Hospital.
what season does meredith and derek get married in grey's anatomy
season seven