Coronal mass ejections (CMEs) are large-scale eruptions of magnetized plasma from the Sun, while their heliospheric counterparts, interplanetary CMEs (ICMEs), are primary drivers of space weather. Understanding their thermal and turbulent evolution is crucial for constraining plasma heating and cooling during expansion and improving space-weather predictions. However, these aspects remain poorly characterized between the inner corona and 1 au. This thesis investigates the thermodynamic and turbulent properties of CMEs/ICMEs in the inner corona and heliosphere using multi-wavelength imaging, spectroscopy, multispacecraft in-situ observations, and geometrical modelling. First, the thermodynamic evolution of a CME core in the inner corona (1.05–1.35 R☉) is investigated using MLSO/K-Cor polarized-brightness observations, MLSO/CoMP Fe XIII 10747 Å spectroscopy, and differential emission measure analysis of SDO/AIA extreme-ultraviolet observations. Its nearly constant million-degree temperature despite declining density indicates near-isothermal evolution, suggesting ongoing heating during expansion. Extending the investigation into the heliosphere, near-radially aligned multispacecraft observations establish the radial evolution of the sizes, plasma, and magnetic properties of the sheath and magnetic-cloud-like (MCL) ejecta. Combined with near-Sun observations and ellipse evolution modelling, the results reveal that MCL ejecta, traditionally attributed to flank encounters with isolated CMEs, can also arise from interactions between closely launched CMEs. Polytropic analysis further identifies dual polytropic behaviour in both ICME substructures, consistent with distinct plasma populations from the interacting CMEs. This highlights the potential of polytropic diagnostics for identifying CME–CME interactions when conventional in-situ signatures are inconclusive. Within the ejecta, this contrast weakens with distance, suggesting progressive thermodynamic homogenization during expansion; however, the sheath maintains this contrast out to 1 au. To characterize ICME turbulence, magnetic fluctuation power, spectral indices and breaks, and velocity–magnetic-field correlations are analysed for twelve ICMEs observed by Solar Orbiter between 0.29 and 1 au. The results reveal that the sheath is the most turbulent region at all distances. Compared with the solar wind, ICME substructures consistently exhibit Kolmogorov-like inertial-range spectra, reduced Alfvénicity, and spectral breaks at higher frequencies, supporting the use of these diagnostics for identifying ICME boundaries. Finally, the thesis presents ATHARV, a tool that extrapolates in-situ time series into space using isotropic self-similar expansion while accounting for the aging effect and spacecraft motion during the ICME crossing. Together, these studies provide new insights into the thermodynamic and turbulent properties of CMEs/ICMEs and highlight the role of these diagnostics in understanding their heliospheric evolution