Upon detection of genotoxic or other stress, cells can withdraw from the cell cycle and become senescent, a fate characterized by resistance to apoptosis, organelle dysfunction and pro-inflammatory secretion. Compelling evidence has highlighted a causal role for senescence in driving pathological ageing, alongside dysregulation of molecular pathways including mTOR and sirtuin signalling. In this thesis, I firstly report generation of a novel model of senescence based on acute treatment of primary human fibroblasts with the sirtuin 1/2 inhibitor Tenovin-6 (TnV6), characterized by permanent cell cycle arrest coincident with p21 upregulation and increased secretion of the SASP factor IL-6. Secondly, I used a range of senescence models and a panel of mTOR inhibitors to investigate mTOR signalling in senescence. Notably, acute treatment of senescent fibroblasts with the pan-mTOR inhibitor AZD8055 reversed multiple senescence phenotypes, including suppression of pro-inflammatory secretion, reduction in actin stress fibres, activation of mitophagy, decreased cellular hypertrophy and the stabilisation of nuclear structure. Furthermore, AZD8055 treatment also disrupted induction of senescence-associated proliferation arrest in a range of models of senescence including DNA damage-induced senescence, coincident with preventing upregulation of p21. In cells approaching replicative senescence, AZD8055 treatment substantially increased the replicative capacity; treatment also stabilized telomere length, in both wild-type and Werner syndrome patient fibroblasts. In addition, I created an unbiased molecular profile of replicative senescence using comparative proteomics, revealing the importance of actin remodelling in senescence, and its regulation through mTOR signalling. I subsequently noted a functional role for senescence-associated dysregulation of cytoskeletal remodelling in orchestrating direct cell-cell contact, and observed intercellular organelle transfer. My findings highlight mTOR signalling as a master regulator of both cell-autonomous and non-cell-autonomous aspects of cellular senescence.