Sina Ruth Greenwood is a New Zealand mathematician whose interests include continuum theory, discrete dynamical systems, inverse limits, set-valued analysis, and Volterra spaces.^[1][2] She is an associate professor of mathematics and Associate Dean Pacific in the faculty of science at the University of Auckland.^[1]

Greenwood's parents emigrated from Samoa to Whanganui in New Zealand, shortly before Greenwood was born; they moved from there to Auckland when she was a child. She earned a bachelor's degree at the University of Auckland, and after some time in Australia became a secondary school teacher in Auckland.^[2]

Returning to the University of Auckland for graduate study in mathematics, she earned a master's degree and then completed her PhD in 1999, under the joint supervision of David Gauld and David W. Mcintyre. Her dissertation was Nonmetrisable Manifolds.^[2][3][4] She and three other students who finished their doctorates at the same time became the first topologists to earn a doctorate at Auckland.^[2]

After postdoctoral research, funded by a New Zealand Science and Technology Post-Doctoral Fellowship, she obtained a permanent position at the University of Auckland as a lecturer in 2004,^[2][5] later becoming an associate professor.^[2] Beyond mathematics, her work at the university has also included advocating for the interests of Pasifika and Māori students.^[2][5]

Greenwood is a Fellow of the New Zealand Mathematical Society,^[6] elected in 2018.^[2]