Abstract: A variety of polymer manifolds and associated fabrication methods are described. The described manifolds can be used in heat exchangers and a variety of other applications. In one aspect a polymer manifold is formed by welding distal tips of a multiplicity of polymer tubes to a polymer retainer. The tubes pass through guide passages that extend between opposing faces of the retainer and the distal tip of each tube is welded to a manifold face of the retainer. The welds between the tubes and the manifold face form sealed connections between the tubes and the manifold face. In some embodiments a locking plate is positioned adjacent the retainer. The tubes also pass through the locking plate such that during assembly, the locking plate and/or the retainer can be translated or otherwise moved slightly relative to the other to hold the tubes in place during welding to the retainer.