A combined use of fluorescence and light microscopy is a powerful approach to further increase our understanding in biological systems of structure-function relations at cellular and sub-cellular levels. The power of fluorescence microscopy (FM) is to spectrally resolve and visualize individual proteins with endogenous or immuno- fluorescent labeling. Additionally, super-resolution microscopy techniques have beaten the diffraction limit and improved the achievable resolution in FM down to sub 20 nm. However, inherent to FM, it is only the labelled components that are visible and FM cannot provide the ultrastuctural information. On the other hand, electron microscopy (EM) has the power to visualize the ultrastructure with nanometer scale resolution. Therefore, correlative light and electron microscopy (CLEM), which brings the complementary information from FM and EM together, has gained deep interest in recent years. CLEM studies are typically carried out sequentially, by transferring the sample between two separate microscopes, which makes the process considerably cumbersome and therefore constrain widespread CLEM applications. A solution is proposed by integrated strategies, in which a light microscope is mostly integrated in an EM. We have also recently presented an integrated microscope design which enables high-resolution FM inside a Scanning EM (SEM) without compromises in the capabilities of both microscopes. This thesis aims to explore the potential of the integrated microscope for linking spectrally resolved and live-cell imaging capable FM with structural and high-resolution EM. The novel possibilities introduced by the integrated microscope are presented and discussed firstly for fixed and dehydrated samples, as typical samples in CLEM studies. Furthermore, CLEM of samples in hydrated conditions is realized, and a novel method, which enables on-demand SEM of living cells in liquid is demonstrated. Chapter II. introduces the method of Simultaneous Correlative Light and Electron Microscopy (SCLEM), which is a novel approach to CLEM brought up by the integrated microscope. The method is based on the new possibility to carry out both high-resolution light and electron microscopy simultaneously to the same region of a sample. The method makes it possible for fast and accurate acquisition of large CLEM datasets, and therefore for quantitative investigations of large sample areas. The correlation of high-NA fluorescence imaging with cellular ultrastructure is demonstrated for fluorescently labelled whole cells, as well as tissue sections stained both fluorescently and for EM. The optimized protocol for SCLEM, which aims to help other researchers to adapt their workflows to integrated CLEM, is presented in Chapter III. The complete sample preparation protocols for whole cells expressing endogenous fluorophores, for whole cells with immuno-labelling, and for resin embedded cells and tissues are presented together with the mounting procedure for the prepared samples in the integrated microscope. Also the imaging steps required to assure high accuracy registration between the FM and SEM images are explained and demonstrated comprehensively. Chapter IV. presents the enrichment of SCLEM with multi-color capabilities. Simultaneous dual-color FM and SEM is demonstrated by imaging cellular sections of Equine Arteritis Virus (EAV) infected cells, where EAV expresses GFP from its replicase gene and the nuclei/DNA of the infected cells are labelled with Hoechst. The chapter also shows that the method for FM-SEM image registration can also be used for chromatic distortion correction in between distinct FM color channels, which is crucial if the fluorescence information will be mapped onto high-resolution SEM images. The presented method is demonstrated by registering dual-color fluorescence images and a SEM images of paxillin and phospho-paxillin labelled cells into a single coordinate frame with a high precision. The rest of this thesis focuses on CLEM of samples in liquid, encapsulated in the integrated FM and SEM. Chapter V. investigates the achievable resolution in SEM imaging of liquid-immersed nanoparticle bio-labels in detail. Simulations with the Geant4-based Monte Carlo scheme are directly compared to the experimental results for nanoparticles located directly beneath SiN membranes of different thicknesses. The beam broadening, resulting from the interaction of the electron beam with the membrane, and the contrast forming mechanism was discussed and characterized. Also in liquid- SCLEM imaging of single epidermal growth factor (EGF) conjugated quantum dots docked at filopodia during cellular uptake is presented. Furthermore, the resolution and contrast for imaging nanoparticle bio-labels located not directly beneath the membrane but at different depths are investigated in Chapter VI. Some initial simulation and experimental results are presented which already shows that imaging single nanoparticle bio-labels is still feasible with reasonable resolution even under these conditions. The design and fabrication processes of the holder used for CLEM of liquid samples are presented in Chapter VII. The holder encapsulates liquid samples in the vacuum chamber of the integrated microscope and enables simultaneous correlative microscopy through the electron transparent and the light transparent windows it has. The detailed sample preparation process for correlative imaging of whole cells cultured directly on the electron transparent membranes, which brings new possibilities to study cells in their near native environment, is represented. Also the possibility of advancing the holder to a microfluidic reactor is discussed and proof-of concept experiments with consecutive filling and imaging in the reactor are demonstrated. Finally, Chapter VIII. presents the novel method of on-demand EM (ODEM), which merges the strengths of live-cell FM imaging with high resolution SEM. The cellular dynamics are monitored in liquid with live-cell FM, and SEM snapshots are captured at selected regions and time-points on-demand, based on the FM observations. ODEM is demonstrated by imaging the uptake and retrograde transport of EGF-conjugated quantum dots (QDots) in fibroblasts. ODEM is promising for opening up entirely novel perspectives for imaging biological dynamics by linking the live cell imaging capabilities of FM with high resolution structural EM imaging.