The tropicalization of a subvariety of an algebraic torus is a polyhedral complex in R^n. There are naturally defined weights on the faces which satisfy a constraint called the balancing condition. We will discuss tropicalization for curves and how divisor relations on a toric variety lead to the balancing condition. We will then discuss a generalisation of the above setting by considering subvarieties of torus bundles. The usual balancing condition does not always hold but an analogue may be formulated.