In the past two decades, we have seen an unprecedented rise in unlicensed wireless devices and applications of wireless technology. To meet various application constraints, we continually customize the radios and their protocols to the application domain which has led to significant diversity in spectrum use. Unfortunately, this diversity (coupled with increased demand) complicates spectrum sharing, exacerbates interference, and as a result: reduces network performance and capacity. The introduction of the "white spaces" to address the increasing demand for spectrum further complicates this problem. Now, unlicensed devices must also adhere to strict regulations against interference on "spectrum primaries," i.e., licensed devices in these bands. In an attempt to address diversity between devices in unlicensed spectrum, our community has focused on developing coexistence techniques, i.e., modifications to the radios and protocols to reduce interference between two specific technologies when operating in the same band. This general approach, however, requires N[superscript 2] solutions, that are rarely deployed and often short-lived due to rapid changes in unlicensed technologies. To address diversity with spectrum primaries in the white spaces, spectrum management approaches are being enforced that are effective but extremely spectrum inefficient, threatening the very the goal of the white spaces: additional spectrum. In this dissertation, we explore alternative approaches. We argue that spectrum management can be a better long-term solution to address diversity between technologies sharing unlicensed spectrum, whereas coexistence techniques can provide spectrum-efficient solutions to protect spectrum primaries. However, one cannot simply apply white space spectrum management techniques to unlicensed spectrum due to a lack of information and algorithms that support the high degree of unlicensed technologies. Similarly, traditional coexistence techniques between unlicensed devices do not meet strict zero-interference policies to be applied to spectrum primaries. To overcome these challenges and provide more efficient and long term solutions to interference between heterogeneous technologies, we make three key contributions in this dissertation. First, we introduce a novel system on the smartphone which allows it to collect the necessary information about heterogeneous wireless technologies towards proper spectrum management between unlicensed devices. Using this information, we then introduce an efficient and effective spectrum assignment model and algorithm, capable of supporting various unlicensed technologies (even as they evolve). Finally, we switch our focus to the white spaces and show how spectrum management is spectrum inefficient to be effective, and introduce a novel coexistence protocol between unlicensed devices and spectrum primaries that allows spectrum-efficient interference-free coexistence. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]