Given an undirected graph G = (V, E) with nonnegative costs on its edges, a root node r ∈ V , a set of demands D ⊆ V with demand v ∈ D wishing to route w(v) units of flow (weight) to r , and a positive number k, the Capacitated Minimum Steiner Tree (CMStT) problem asks for a minimum Steiner tree, rooted at r , spanning the vertices in D ∪ {r }, in which the sum of the vertex weights in every subtree connected to r is at most k. When D = V , this problem is known as the Capacitated Minimum Spanning Tree (CMST) problem. Both CMsT and CMST problems are NP-hard. In this article, we present approximation algorithms for these problems and several of their variants in network design. Our main results are the following:-We present a (γρ ST + 2)-approximation algorithm for the CMStT problem, where γ is the inverse Steiner ratio, and ρ ST is the best achievable approximation ratio for the Steiner tree problem. Our ratio improves the current best ratio of 2ρ ST + 2 for this problem. -In particular, we obtain (γ +2)-approximation ratio for the CMST problem, which is an improvement over the current best ratio of 4 for this problem. For points in Euclidean and rectilinear planes, our result translates into ratios of 3.1548 and 3.5, respectively. -For instances in the plane, under the L p norm, with the vertices in D having uniform weights, we present a nontrivial ( 7 5 ρ ST + 3 2 )-approximation algorithm for the CMStT problem. This translates into a ratio of 2.9 for the CMST problem with uniform vertex weights in the L p metric plane. Our