The traditional pen-paper sketching is extensively used in the early stages of product design as it supports creative exploration of product concepts and provides a fluidic mode for the expression of ideas. The Computer Aided Design (CAD) models support the later stages of design and manufacturing process. Faithful conversion of the designer’s ideas from concept sketches to the CAD models is a skill intensive and time consuming exercise which reduces the overall productivity of the organization. Providing computer based support can help the designer, in several ways, by reducing demand on the skill and allow focusing more on creative exploration of the concepts. Towards that, the thesis presents methodologies to understand the product concept sketches, support cognitive activities like perceiving the composition and behaviour, and create and interact with the sketches, directly in 3D. To begin with, traditional 2D sketches of product concepts are studied mainly to explores the psychological (cognitive) and physiological (musculoskeletal) activities of the designer in the context of the product being designed. A sketching application is created for capturing the sketches created using a tablet in digitized form. The captured data is analyzed based on the identified parameters. A grouping methodology is devised to group the stroke based on the observations which are akin to Gestalt laws of perceptual organization. This functional grouping or segmentation is used to identify the mental model of the product concept and the design rationale behind it. In concept sketches, annotations carry information like behaviour, functionality and usage. These wishful declarations need to be verified through simulation! To simulate the behavior of the components identified by the functional segmentation method, a kinematic model is defined where the designers interactively describe the constituents like joints, fixed links, inputs, etc. The interactive simulation changes the underlying kinematic model and makes the sketches to move to show the behavior. This system also provides methods to verify boundary constraints and allows creating patterns. Traditional 2D sketching suffers from several deficiencies. To overcome these, a novel direct 3D sketching methodology is proposed with stereo vision and haptic feedback. Different types of strokes creations like curves, strips and sweep surfaces, directly in 3D space, are demonstrated. Further, to provide control over stroke creation process, visual and haptic feedbacks are studied. Haptic rendering schemes for stroke generation are explored based on mechanics of sketching. Using the curve generation methods, surface generation schemes are devised. Mainly two types of schemes are explored (a) sweep surface and (b) Hatching surfaces. To support constrained concept exploration, two types of haptic constraints are modeled and their application is demonstrated in constraining a sketch within a boundary and outside a boundary. Motion constraints are implemented by simulating the behaviour of identified components’ motions. Two types of motion are implemented (a) Linear translation and (b) Rotation about an axis. Finally, a sketch based distributed collaboration method is presented to enable design interaction in the context of global product development. Several issues related to the realization of a sketch based collaborative conceptual design system are explored and, one such instance is demonstrated through experiments.