The main goal of this dissertation is to develop simple and accurate models for the transient monotonic and cyclic deformation behaviour of bitumen and asphalt mixes. The first part of this dissertation is concerned with an experimental and theoretical investigation of the deformation behaviour of bitumen. The second part is concerned with the deformation of bituminous mixes. A brief description of the main literature on composition, structure and mechanical behaviour of pure and polymer-modified bitumens is presented in chapter 2. An extensive experimental study comprising of monotonic, continuous cyclic and pulse loading tensile experiments for two pure and two polymer-modified bitumens is detailed in chapter 3. Based on these experimental findings a simple constitutive phenomenological model including the effects of rate dependent recovery is proposed for bitumen. Comparisons between experiments and model predictions are presented with good agreement. The spherical indentation behaviour of bitumen under monotonic and cyclic loading conditions is studied in chapter 4. A simple extension to the power-law indentation model of Bower et al. (1993) is proposed for bitumen with good agreement with experimental results. Chapter 5 presents a review of the main research on continuum and micro-mechanical models for the deformation behaviour of bituminous mixes. An extensive experimental investigation of the monotonic and cyclic compressive deformation behaviour of bituminous mixes with varying volume fractions of aggregate, for uniaxial and triaxial conditions, is described in chapters 6 and 7, respectively. An extension to the phenomenological model proposed for bitumen is proposed for these mixes. The predictions of the model are compared with the experimental results with good agreement. In chapter 8, a micro-mechanical constitutive model for the deformation behaviour of asphalt is assembled using micro-mechanical theories and experimental observations. The model predictions are compared with uniaxial and triaxial experimental results, showing reasonably good agreement. Finally, conclusions and recommendations for future work are presented in chapter 9.