Most research on preference elicitation, preference rea- soning and preference query languages design focus mainly on preferences over single objects represented by relational tuples. An increasing interest on preferences over more complex structures like sets of objects has arised in recent papers. However, most recent applications deal with more sophisticated complex structured objects, like sequences, trees and graphs. In this paper, we introduce TPref, a for- malism to reason with qualitative conditional preferences over sequences of objects indexed in time. TPref gener- alizes the CP-Nets formalism by allowing temporal condi- tional preferences besides the static rules used in CP-Nets. An algorithm for computing optimal sequences of objects satisfying a set of temporal constraints is also presented.