Basics.- I. Part A: Introduction to random walks.- B: The physical mechanisms of anomalous diffusion.- II. Fractals and multifractals in physics.- III. Hydrodynamics at low Reynolds numbers: a brief and elementary introduction.- IV. Some chemical engineering problems related to mixing and disorder.- Short contribution: 1. Chemical dissolution of a porous medium: experiments and computer simulations.- Dispersion.- V. Experimental study of tracer dispersion in model and natural porous media.- VI. Dispersion in porous media.- VII. Hydrodynamic dispersion in random networks.- VIII. Pollutant dispersion in oceans.- Short contributions: 2. Diffusive transport in laminar flows.- 3. Diffusive transport in the Rayleigh-Benard convective flow.- 4. Logarithmic effects in longitudinal dispersion in porous media.- Suspensions.- IX. Sedimentation of small particles.- X. Filtration processes.- XI. Aspects of flow and mixing behavior in fluidized beds.- Mixing in complexe situations.- XII. Transport of polymers.- XIII. Mass transfer and reaction in fixed-bed heterogeneous systems: application to sorption operations and catalytic reactors.- XIV. The effect of dispersion on fingering in miscible displacements.- XV. Two phase flow through packed bed static and dynamic accessibilities of the packing.- Short contributions: 5. Mixing in agitated vessels: a random-walk approach.- 6. Elastohydrodynamic collisions and bouncing of spherical particles.- 7. Hintered settling and hydrodynamic dispersion of sedimenting spheres.- Turbulence and reactions.- XVI. Molecular mixing and chemical reactions in turbulent shear flows.- XVII. Theory of flames.- Short contribution: 8. Intermittency in boundary layer.- Techniques.- XVIII. Magnetic resonance imaging of liquids in porous media: a comparison to other visualization techniques.- XIX. Stereological analysis of condensed materials.- Conclusion.- XX. Lagrangian mixing.- Index of key words.