Zachary John Lemnios (born February 21, 1955) is an American scientist, executive, and engineer who has worked in government, industry, and academia. Most notably, he held the post of Assistant Secretary of Defense for Research and Engineering (currently known as Under Secretary of Defense for Research and Engineering) from 2009 to 2012, and he has served as the first Chief Technology Officer of MIT Lincoln Laboratory, and as Vice President of Research at IBM. Lemnios later founded ZJL Consulting, LLC.