Abstract: 
This talk will give an introduction to knot theory in four-space. We will see that any knot can be deformed to a simple unknotted circle without having any self-intersections at any time. Thus, the theory of knotted circles in dimension four is not very interesting. On the other hand, surfaces like the sphere and the torus can be knotted in four-space. We will discuss a few ways to construct interesting surface-knots from the trefoil knot and how to visualize them. Time permitting, we will also take a closer look at a particular surface-knot and discuss ways to distinguish it from other knots.