  The subject of this thesis is the construction and the study of
four-dimensional effective theories with spontaneously broken and non-linearly
realised global and local supersymmetry. In the first part, the global
supersymmetric case is analysed. The discussion starts from the supersymmetry
breaking sector, describing the goldstino and its interactions, in the case of
minimal supersymmetry and it is then generalised to a generic number of
spontaneously broken supersymmetry generators. A systematic procedure is given
in order to construct effective theories with non-linearly realised
supersymmetry and with any desired spectrum content. In the second part of the
thesis, non-linear realisations are analysed in the case of local
supersymmetry, namely supergravity. The coupling of the goldstino sector to
gravity is presented first and the superhiggs mechanism on a generic background
is discussed. Matter couplings are then constructed in some simple examples. A
new class of models is introduced in which supersymmetry is spontaneously
broken and non-linearly realised already on the gravity sector. As a
consequence, it is possible to construct actions in which the cosmological
constant is bounded to be positive, which can be motivated for studying
inflation. Two applications of non-linear realisations in local supersymmetry
are discussed in detail. In the first one it is shown how to implement K\"ahler
invariance in a way that mimics the global supersymmetric case. In particular,
the K\"ahler--Hodge restriction on the scalar manifold, which is typical of
supergravity, is avoided. In the second application the role of non-linear
realisations in the construction of de Sitter vacua is discussed. Attention is
devoted to the relationship with known de Sitter uplift constructions and with
a new, recently proposed D-term in supergravity.
