| Term | Definition |
| Lewis and Clark | leaders of an expedition commissioned by President Jefferson, who explored uncharted territories and helped lay the foundations for western expansion. |
| Aaron Burr | ran against Thomas Jefferson for the presidency; received the same number of electoral votes as Jefferson; Burr became Vice President after Alexander Hamilton convinced Federalists to vote for Jefferson |
| John Marshall | staunch Federalist judge appointed Chief Justice of the Supreme Court by Adams |
| Judiciary Act of 1801 | a law that increased the number of federal judges, allowing President John Adams to fill most of the new posts with Federalists |
| midnight judges | one of the judges appointed by John Adams in the last hours of his administration |
| Marbury v. Madison | an 1803 case in which the Supreme Court ruled that it had the power to abolish legislative acts by decairng them unconstitutional; this power came to be known as judicial review |
| judicial review | the Supreme Court's power to declare an act of Congress unconstitutional |
| Louisiana Purchase | the 1803 purchase by the US of France's Lousiana Terrority- extending from the Mississippi River to the Rocky Mountains for $15 million |
| Sacajawea | Native American Shoshone woman, 15, who served as a guide and interpreter for the Lewis and Clark expedition |