Lean is a culture-based management system essentially aimed at waste elimination, thereby creating value for the customer. It is a transformation journey and to evaluate the progress on this journey at any time, the achieved state of maturity has to be assessed. We argue that Lean Construction management spans three stages or phases - Physical (Activity-based) Manifestation, Behavioral (Culture-based) Manifestation and Strategic (Long-term) Manifestation. To evaluate the progress on this journey and assess the state of Lean maturity achieved across a project or the entire organization at any stage, a host of factors needs to be considered. The distinctive factors relating to each of the above three stages are initially identified by literature survey and interviews. These factors are then assigned with different individual weights through findings from a detailed questionnaire survey. A weighted factor model is then developed to assess the overall maturity at project and organizational levels. The Lean scores for the various factors are shown on a Spider Radar and a bar chart and overall maturity level is plotted on a normative Lean maturity progression curve spanning across the three stages. The model was developed based on data collected from 25 Lean practitioners across six organizations, which are implementing Lean construction in their sites. The model was then applied to projects of four different organizations and the Lean Construction Maturity Ratings were calculated. These scores were then discussed with experts to validate whether the scores appropriately reflected, in an overall qualitative sense, the Lean maturity of the projects surveyed. In view of the low level of spread of Lean practices across the Industry in this country, assessment of Lean maturity across an entire organization has not been taken up so far.