Erasmus Smith's Professorship of Natural and Experimental Philosophy is a chair in physics at Trinity College Dublin. It was founded in 1724 and funded by the Erasmus Smith Trust, which was established by Erasmus Smith, who lived 1611–1691.
From 1724 to 1847 the chair had a mathematical and theoretical orientation, with many holders being also mathematicians, and several such as Bartholomew Lloyd (1822) and James MacCullagh (1843) having previously held the Chair of Mathematics. Then in 1847 the University Chair of Natural Philosophy (1847) was founded and took on the applied mathematics and theoretical physics role, while Erasmus Smith's Professorship became the chair of experimental physics.