  Modern software engineering deals with demanding problems that yield large
and complex software. The area of Model-Driven Software Engineering tackles
this issue by using models during the development process, but it does not
address some of the communication problems among different stakeholders.
Domain-Specific Modelling Languages (DSML) aim at involving domain experts with
non-technical profiles in that process.
  DSMLs define concepts with different levels of abstraction, but traditional
modelling does not allow enough flexibility to organise them adequately.
Multilevel Modelling (MLM) approaches provide an unbounded number of levels of
abstraction, plus other features that perfectly fit DSMLs. Their development
can also benefit from Model Transformations (MT), especially when these encode
the behaviour of DSMLs. MTs can be exploited by MLM, becoming a precise and
reusable definition of behaviour.
  This thesis presents a MLM and Multilevel MT approach which tackles open
issues in the field and compares it with the state of the art through
literature review and experiments, providing its formalisation and its
implementation in the tool MultEcore, together with case studies.
