In this chapter, you will be introduced to different mechanisms that contribute to the signal in nonstationary tissues, such as blood within vessels, which can produce high-quality diagnostic magnetic resonance angiography (MRA). We will discuss blood flow dynamics and how the inherent motion of moving spins can produce endogenous contrast-enhanced angiographic images using two major imaging sequences. We will examine how spin echo (SE) and gradient echo (GRE) imaging produce dark and bright signals due to the time-of-flight (TOF) effect, which relies on flow-dependent changes. We will also explore phase-contrast (PC) imaging and how gradient moment nulling and velocity encoding gradients can suppress flow-related artifacts, allowing us to quantify physical quantities such as velocity and generate 3D PC MRA. Finally, we will discuss the basics of contrast-enhanced MRA, including how exogenous substances are injected to alter tissue properties, producing MRA images, and how different concentrations of gadolinium and injection rates change the T1 and T2* of blood, making them suitable for rapid MRA. In addition, we will also see how new imaging techniques, along with artificial intelligence, have advantages in reducing contrast dosing and still give us diagnostically high-quality images with shorter scan times.