A beamline for attosecond time-resolved soft-X-ray spectroscopy up to the oxygen K-edge (~540 eV) has been developed. This beamline has been applied to realize the first attosecond transient-absorption experiments at the carbon K-edge. We have studied the dynamics following strong-field ionization of ethylene in the gas phase. This has led to the observation of the D1D0 electronic relaxation of the ethylene cation in less than 7 fs, which is the fastest electronic relaxation dynamics observed to date. Comparison with detailed quantum-dynamics simulations has revealed ballistic motion across a conical intersection to be responsible for this extremely fast and efficient process. Promising results have also been obtained on the methane and ethane cations. A second beamline for X-ray absorption spectroscopy equipped with a flat microjet has also been developed. This setup has been used to demonstrate extreme-ultraviolet high-harmonic generation for the first time. The properties of high-harmonic generation in liquids have been characterized in detail, including the scaling of the cut-off and yield with driving intensity, the ellipticity dependence of the harmonic yield and the coherence of the high-harmonic emission. More recently, the polarization and the wavelength dependence of HHG in liquids have also been studied. Moving on from high-harmonic spectroscopy to X-ray absorption spectroscopy, we have obtained the first femtosecond time-resolved spectra in the soft-X-ray domain from a liquid target. Specifically, we have studied the electronic and nuclear dynamics following the ionization of liquid methanol and pyridine. Turning from absorption to photoelectron spectroscopy, we have completed the first attosecond time-resolved measurements in liquids by measuring photoemission delays of 50-70 attoseconds between liquid and gaseous water. The interpretation of this measurements has shown that the delays are dominated by solvation effects, i.e. they probe the influence of the liquid environment on the photoionization delays of water molecules. In a complementary experiment based on electron-ion-coincidence spectroscopy, we have measured photoionization delays as a function of the size of water clusters. We have found that the delays correlate linearly with the spatial extension of the electron hole quantified as the first moment of the electron-hole density. This result confirmed the interpretation of the liquid-phase results and provided a molecular-level understanding of attosecond photoionization dynamics of liquid water. Using electron-electron coincidence spectroscopy, we have realized the first observation of intermolecular Coulombic decay in liquid water and have compared the corresponding electron spectra with those of water clusters. Finally, returning to the gas phase, we have observed attosecond charge migration in a neutral molecule, its de- and recoherence caused by nuclear wave-packet motion and the transfer of electronic coherence through a conical intersection.