We introduce the notion of a symmetric Whitney tower cobordism between bordered 3-manifolds, aiming at the study of homology cobordism and link concordance. It is motivated by the symmetric Whitney tower approach to slicing knots and links initiated by T. Cochran, K. Orr, and P. Teichner. We give amenable Cheeger-Gromov ρ-invariant obstructions to bordered 3manifolds being Whitney tower cobordant. Our obstruction is related to and generalizes several prior known results, and also gives new interesting cases. As an application, our method applied to link exteriors reveals new structures on (Whitney tower and grope) concordance between links with nonzero linking number, including the Hopf link.License or copyright restrictions may apply to redistribution; see http://www.ams.org/journal-terms-of-use 3242 JAE CHOON CHA Cheeger-Gromov ρ-invariants due to Orr and the author [CO12]. As a new application that known Whitney tower frameworks do not cover, we study concordance between links with nonzero linking number. In particular we investigate Whitney tower and grope concordance to the Hopf link.Symmetric Whitney tower cobordism of bordered 3-manifolds. First we briefly introduce how we adapt the Whitney tower approach in [COT03] for homology cobordism of bordered 3-manifolds.Recall that a 3-manifold M is bordered by a surface Σ if it is endowed with a marking homeomorphism of Σ onto ∂M . For 3-manifolds M and M bordered by the same surface, one obtains a closed 3-manifold M ∪ ∂ −M by glueing the boundary along the marking homeomorphism. A 4-manifold W is a relative cobordism. Initiated by S. Cappell and J. Shaneson [CS74], understanding homology cobordism of bordered manifolds is essential in the study of manifold embeddings, in particular knot and link concordance. This also relates homology cobordism to other key problems including topological surgery on 4-manifolds.As a surgery theoretic Whitney tower approximation to a homology cobordism, we will define the notion of a height h Whitney tower cobordism W between bordered 3-manifolds (h ∈ 1 2 Z ≥0 ). Roughly speaking, our height h Whitney tower cobordism is a relative cobordism between bordered 3-manifolds, which admits immersed framed 2-spheres satisfying the following: while the 2-spheres may not be embedded, they support a Whitney tower of height h, and form a "lagrangian" in such a way that if the 2-spheres were homotopic to embeddings, then surgery along these would give a homology cobordism. For a more precise description of a Whitney tower cobordism, see Definition 2.7.It turns out that a height h Whitney tower cobordism can be deformed to another type of a relative cobordism satisfying a twisted homology analogue of the above Whitney tower condition, which we call an h-solvable cobordism. Roughly speaking, it is a cobordism which induces an isomorphism on H 1 and admits a certain "lagrangian" and "dual" for the twisted intersection pairing associated to (quotients by) derived subgroups of the fundamental group. See Definition 2.8 and Theorem 2.9 for details. ...