The development of practical DNA-based applications in bio- and nanotechnology has uncovered a menagerie of complications, many related to interactions of molecules with surfaces. Fortunately, the tools and methods developed or adapted for analyzing DNA and other biointerfaces are now significantly advanced to make an impact in both basic and applied surface science of DNA. I will focus on the progress in understanding DNA-surface and DNA-DNA interactions resulting from our ex-situ spectroscopic studies by XPS, FTIR, and NEXAFS. Homo-oligonucleotides have emerged as a useful model system for the study of such interactions. A few examples from the surprisingly wide range of phenomena that we have uncovered include polyelectrolyte behavior of weakly-interacting oligo(dT) strands, buffer-induced cross-linking in oligo(dC) films, and singularly high affinity of oligo(dA) for gold. The most practical impact of our analysis of DNA-functionalized surfaces has been quantifying the effects of experimental conditions (concentration, temperature, buffer salt, etc.) on DNA immobilization and hybridization. Improved understanding of nucleobase-dependent interactions should also facilitate the rational design of immobilization chemistries and DNA probe sequences. Ultimately, the challenge is to apply surface science methods to more complex biomolecular systems and processes, such as label-free characterization of DNA hybridization. @FootnoteText@ This work was done in close collaboration with A. Opdahl, H. Kimura-Suda, V. Perez-Dieste, J. M. Sullivan, F. J. Himpsel, M. J. Tarlov, and L. J. Whitman.