Cold atmospheric pressure plasma (CAP) is an excellent source of reactive species because they are able to produce these species cheaply, in a variety of configurations, and in a way that can be distributed easily but there needs to be more understanding of how they specifically interact with surfaces. The goals of this dissertation are to understand what the critical reactive species reaching a surface are for particular applications. As a first step we find that a plasma in direct electrical contact with a polymer material shows high etching rate and non-uniform treatment whereas a remote regime treatment can lead to a relatively uniform treatment over the exposed to plasma area. The interaction of vacuum ultraviolet (VUV) light with polymer surfaces was found to be critical under conditions where local oxygen is displaced by noble gas flow. This VUV flux is also dependent on plasma source type, being highest for high voltage sources using noble gas flow. For a surface microdischarge (SMD) source we find high activation energy compared with atomic oxygen etching suggesting less reactive species reaching the surface are causing surface modification. However, for an atmospheric pressure plasma jet (APPJ) source we find that the activation energy changes over treatment distance, decreasing below the value expected for atomic oxygen as the jet gets closer to the surface. Additionally we find evidence of directional etching for the close distances which becomes less directional for further distance treatments suggesting we have a contribution from high energy species at closer distances despite there being no visible contact between the plasma plume and the polymer surface. Nickel catalyst materials interacting with plasma can be enhanced to show increased breakdown of methane and production of different product species such as CO compared to just the catalyst. This catalyst material also shows carbon deposition by CO and COO- groups by plasma treatment, though increased plasma power and temperature can then remove these groups as well.