Lewis has pointed out that – largely because his career began when the field of computer science "barely existed", and Harvard offered almost no computer science courses at the undergraduate level – he originated almost all the courses he has taught.
It was his proposal, in the late 1970s, that Harvard create a major specifically for computer science
(which until then had been a branch of Harvard's applied mathematics program).

From 2003 to 2008 he was designated a Harvard College Professor in recognition of "particularly distinguished contributions to undergraduate teaching".

Six of his teaching assistants are now members of the Harvard faculty and many others are professors of computer science (or related disciplines) elsewhere;
many have gone on to win teaching awards themselves, including Eric Roberts (Association for Computing Machinery Karlstrom Award), Nicholas Horton (Robert V. Hogg Award), Joseph A. Konstan (University of Minnesota Distinguished University Teaching Professor, Graduate/Professional Teaching Award), and Margo Seltzer (Herchel Smith Professor of Computer Science at Harvard, Phi Beta Kappa teaching award, Abramson Teaching Award).

His undergraduate students have included Mark Zuckerberg (whose website "Six Degrees to Harry Lewis" was a precursor to Facebook – six degrees being a reference to the small world hypothesis),Microsoft founder Bill Gates (who solved an open theoretical problem Lewis had described in class), and nine future Harvard professors.

Lewis is the author or coauthor of three undergraduate textbooks:
An Introduction to Computer Programming and Data Structures using MACRO-11 (1981).
MACRO-11 was an assembly language for PDP-11 computers.

Elements of the Theory of Computation (1981, with Christos H. Papadimitriou) covers automata theory, computational complexity theory, and the theory of formal languages; its inclusion of complexity theory and mathematical logic was innovative for its time.
It has been called an "excellent traditional text" but one whose terse and heavily mathematical style can be intimidating.
Although intended for undergraduates, it has also been used for introductory graduate courses.

Data Structures and Their Algorithms (1991, with Larry Denenberg).

Lewis also teaches a course on amateur athletics and the social history of sports in America.
Lewis has pointed out that – largely because his career began when the field of computer science "barely existed", and Harvard offered almost no computer science courses at the undergraduate level – he originated almost all the courses he has taught. It was his proposal, in the late 1970s, that Harvard create a major specifically for computer science
(which until then had been a branch of Harvard's applied mathematics program).
From 2003 to 2008 he was designated a Harvard College Professor in recognition of "particularly distinguished contributions to undergraduate teaching".
Six of his teaching assistants are now members of the Harvard faculty and many others are professors of computer science (or related disciplines) elsewhere;
many have gone on to win teaching awards themselves, including Eric Roberts (Association for Computing Machinery Karlstrom Award), Nicholas Horton (Robert V. Hogg Award), Joseph A. Konstan (University of Minnesota Distinguished University Teaching Professor, Graduate/Professional Teaching Award), and Margo Seltzer (Herchel Smith Professor of Computer Science at Harvard, Phi Beta Kappa teaching award, Abramson Teaching Award).
His undergraduate students have included Mark Zuckerberg (whose website "Six Degrees to Harry Lewis" was a precursor to Facebook – six degrees being a reference to the small world hypothesis),Microsoft founder Bill Gates (who solved an open theoretical problem Lewis had described in class), and nine future Harvard professors.
Lewis is the author or coauthor of three undergraduate textbooks:
An Introduction to Computer Programming and Data Structures using MACRO-11 (1981). MACRO-11 was an assembly language for PDP-11 computers.
Elements of the Theory of Computation (1981, with Christos H. Papadimitriou) covers automata theory, computational complexity theory, and the theory of formal languages; its inclusion of complexity theory and mathematical logic was innovative for its time. It has been called an "excellent traditional text" but one whose terse and heavily mathematical style can be intimidating. Although intended for undergraduates, it has also been used for introductory graduate courses.
Data Structures and Their Algorithms (1991, with Larry Denenberg).
Lewis also teaches a course on amateur athletics and the social history of sports in America.
Harry R. Lewis