Preface. 1. Quantum tunnelling of a macroscopic variable (A.J. Leggett). 2. Quantum tunnelling diffusion in solids (Yu.Kagan and N.V. Prokof'ev). 3. The decay of a metastable state in a multidimensional configuration space (U. Eckern and A. Schmidt). 4. Dissipative quantum mechanics of Josephson junctions (A.I. Larkin and Yu.N. Ovchinnikov). 5. Quantum tunnelling in a high-frequency field (B.I. Ivlev and V.I. Mel'nikov). 6. Macroscopic quantum effects in the current-biased Josephson junction (M.H. Devoret et al.). 7. Theory of nonradiative trapping in crystals (A.S. Ioselevich and E.I. Rashba). 8. Assisted tunneling in metallic systems (A. Zawadowski and K. Vladár). Author index. Subject index. Cumulative index.