The topic of the habilitation thesis are Ekeland type theorems for functions f : X Y and (partial) minimal element theorems for subsets M X × Y , where X is a complete metric or a (sequentially) complete uniform space and Y an arbitrary nonempty set. Two cases of special importance are investigated: Y is an ordered monoid and Y is the power set of a quasiordered linear space, itself quasiordered by the two canonical extensions of the order relation on the linear space to its power set. The proofs of the variational principles are divided in two steps: First, a (partial) minimal element theorem on a metric/uniform space is proven and second, the variational principle is derived as a corollary by introducing a suitable order relation. Almost all known results of the field such as Ekeland's variational principle, Phelps' lemma, Danes' drop theorem, Kirk-Caristi's fixed point theorem and minimal point theorems are generalized considerably in this way. Moreover, new formulations in terms of set relations are given. The thesis starts with a chapter on algebraic and order theoretic properties of power structures. The concept of a (an ordered) conlinear space is introduced as a generalization of a linear space. Set relations on power sets of ordered sets are investigated. The main result is the relationship between minimal/maximal points for the original relation and the infimum/supremum for the set relations.