Originally invented for imaging surfaces, atomic force microscopy (AFM) has evolved into a multifunctional molecular toolkit, enabling us to investigate the interactions of biological systems over scales ranging from single-molecules to whole cells. Specific highlights include the nanoscale imaging of the chemical properties of individual cells, the detection and functional analysis of cell surface receptors using single-molecule force spectroscopy and the quantitative measurement of cellular interactions using single-cell force spectroscopy. These advanced force spectroscopy modalities offer new opportunities for understanding the molecular bases of cell adhesion processes, which is a fundamental challenge in current life science and biotech research.