We give an introduction to the study of algebraic hypersurfaces, focusing on the problem of when two hypersurfaces are isomorphic or close to being isomorphic. Working with hypersurfaces and emphasizing examples makes it possible to discuss these questions without any previous knowledge of algebraic geometry. At the end we formulate the main recent results and state the most important open questions. Algebraic geometry started as the study of plane curves C ⊂ R 2 defined by a polynomial equation and later extended to surfaces and higher dimensional sets defined by systems of polynomial equations. Besides using R n , it is frequently more advantageous to work with C n or with the corresponding projective spaces RP n and CP n. Later it was realized that the theory also works if we replace R or C by other fields, for example the field of rational numbers Q or even finite fields F q. When we try to emphasize that the choice of the field is pretty arbitrary, we use A n to denote affine n-space and P n to denote projective n-space.