This paper presents a unified approach for dynamic modeling and analysis of a biped. A biped is modeled as a floating-base system where the foot-ground interactions are modeled as external forces and moments. Dynamic modeling is proposed using the concept of the Decoupled Natural Orthogonal Complement (DeNOC) matrices. The equations of motion thus obtained are independent of topology of the biped. The advantage of the proposed modeling is highlighted in the paper. A numerical example of a 7-link biped is provided using the methodology presented. Copyright (c) 2010 by JSME.