The chapter presents an overview of the opportunities, challenges and pulse sequence considerations of imaging at low and ultra-low field strengths (defined as less than 1 T in this chapter), i.e., systems lower in field strength than what is used for routine clinical whole-body imaging. A brief description of contemporary commercial and research prototype systems operating in this field strength regime is provided. The pulse sequence considerations and characteristics of MR imaging at these field strengths are discussed, taking into account the relationship between proton relaxation times and signal-to-noise ratio behavior. Leveraging the use of artificial intelligence at different stages of imaging are also discussed. The imaging applications presented within this chapter include both those that are currently approved for clinical use and others that are continuing to be developed under investigational use, and are primarily intended to provide the reader with a preview of the current evolution of MR imaging toward cost-effective, accessible, and sustainable imaging solutions.