Nanoimaging agents have emerged as powerful tools for localized theranostics, including diagnostic imaging and targeted therapy. These nanoimaging agents are designed to deliver therapeutic payloads to targeted disease locations and improve contrast in imaging modalities such as MRI, PET, and CT. Hence, we can simultaneously diagnose, treat, and monitor disease progression. Recent preclinical studies have demonstrated the efficacy of multifunctional nanoparticles in applications such as cancer imaging and therapy. Several organic nanoparticles (NPs), inorganic NPs, and carbon-based NPs have been explored as localized cancer theranostics. They showed promising results with improved selectivity and sensitivity with fewer adverse effects. While many promising nanoimaging agents remain in preclinical development, several formulations have progressed to clinical trials or received regulatory approval. Clinical studies have highlighted both the potential benefits and challenges of translating nanoparticle-based theranostics into human use. Key areas of ongoing research include improving tissue specificity, enhancing detection sensitivity, and optimizing the safety profiles of nanoimaging agents. In this chapter, we will explore the development and application of multifaceted nanoimaging agents for both diagnostic imaging and targeted therapy. We will highlight the novel nanoparticle designs and surface modifications to extend circulation times, improve targeting, and enable multimodal imaging capabilities. Moreover, we will also outline the challenges and future directions for the clinical translation of multifaceted nanoimaging agents.