The extreme progress in high-tech instrumentation has remarkably transformed the way medicine has been practiced making imaging an indispensable foundation for disease diagnosis and treatment. Magnetic Resonance Imaging (MRI) distinguishes itself from other imaging modalities as non-ionizing radiation type of diagnostic imaging, allowing non-invasive visualization and quantification of both anatomical and functional soft tissues features. The introduction of exogenous MR contrast agents has further improved our abilities to target vascular and molecular processes moving from reading images as a result of “an invisible molecular process” to “visualization and quantification of molecular processes” leading to the development of molecular MR imaging. This chapter focuses on the application of MR contrast agents in preclinical studies and how the advancement of their applications has improved our knowledge, especially in the field of oncology. In addition, an overview on the potential environmental impact in the application of MR contrast agents is provided showing how preclinical research could become more environmentally friendly.