The optimization of the properties of the nanomaterials requires in-depth analysis of their structural, morphological and chemical features. In a transmission electron microscope (TEM), combining the classical imaging and spectroscopic modes with the 3D and in-situ approaches allows uncovering materials 3D characteristics, properties and dynamical behaviour. A special focus is put here on three modes : in-situ TEM, quantitative tomography and operando environmental TEM. The in-situ TEM is adapted for assessing the evolution of nanostructures in real time under thermal or electrical constraints, the electron tomography gives access to quantitative analysis of their 3D structural and chemical parameters, whilst the operando TEM offers an elegant solution for solving their behaviour under realistic environmental conditions. For instance, in the field of the heterogeneous catalysis, the analysis of the reaction products by a residual gas analyser simultaneously to the environmental gas TEM study allows us to correlate the microstructural changes in the catalysts with the catalytic activity and selectivity. In electrocatalysis, by tracking the behaviour of electrocatalyst nanoparticles in operando conditions by liquid electrochemical TEM, it was possible to observe the progressive structural transition at the surface of the particles during a potentiodynamic electrochemical measurement. From a fundamental point of view, by applying the liquid TEM to the study of nucleation and growth processes of metal nanoparticles, a typical behaviour consisting in a self-organisation process of molecules in micellar structures, before the particle formation, was evidenced. The aim of this talk is to illustrate through highlighting examples the recent progress in the use of TEM to fulfil the gap between the development of new nanomaterials and nanostructures, their characterization and subsequent properties. More generally, this contribution aims at providing to materials scientists a representative set of studies for illustrating the capabilities of the modern TEMs that can be transposed to their own research.