Economist Marc J. Melitz has returned to Harvard this fall as a full professor after having left campus in 2006 for a two-year stint at Princeton.

Melitz, who is well known for his research on international trade and firm-level responses to trade, was an assistant and associate professor at Harvard between 2000 to 2006.

According to Economics Professor Ariel Pakes, Melitz “changed a whole field with his thesis” that presented a new model for international trade economics.

Economics Department Chair John Y. Campbell said that Melitz’s work has “paid direct attention to the way trade works asymmetrically” and has helped “connect trade theory with applied macroeconomics.” Campbell called Melitz an integral force in the “paradigm shift of the 21st century” in economics.

This semester, Melitz is teaching Economics 1535: “International Trade and Investment,” a course he has taught before as an associate professor at Harvard.

Shankar G. Ramaswamy ’11, who is taking the class this semester, described Melitz as “energetic” as well as “very accessible and patient.”

Ramaswamy said that Melitz has given the course a strong “global perspective” and has “laid the foundation for some of the more specific models” that will be used later in the semester.

Melitz has written two papers with International Trade Economics Professor Elhanan Helpman and is currently working with Pakes on research pertaining to international involvement in the growth of manufacturing in Eastern Europe after the fall of the Berlin Wall.

“I had some very strong ties with colleagues here,” Melitz said, “It feels good to be back.”

He added that he enjoys being back at Harvard “not so much based on working” with specific colleagues but rather on “day to day contact” with other members of the department.

Melitz’s return adds to what Campbell called an “already outstanding group of international economists.”

“I have had the amazing opportunity of being at two places, here and Princeton, that I consider two best places in the world to do work in trade,” Melitz said.

Campbell said that he is glad Harvard “managed to lure [Melitz] back.”

“There is no doubt we now have the best international economics department in the country. It’s a very exciting team,” he said.