Lime (Citrus latifolia Tan.) is a citrus fruit marketed worldwide. Its processing generates a large amount of waste, of which approximately 50% is represented by bagasse (endocarp and mesocarp). The extraction of bioactive compounds from waste is a strategy to recover and add value to the agro-industrial by-products. Pressurized Liquid Extraction (PLE) and Ultrasound Assisted Extraction (UAE) are emerging techniques for obtaining bioactive compounds from plant matrices. Thus, the objective of this work was to compare different extraction techniques to obtain phenolic compounds from agro-industrial lime by-product. The extraction solvent was a mixture of ethanol and water (3:1, m/m), except for Soxhlet, which used pure ethanol. PLE was carried out at 10 MPa, 60, 85, and 110 °C, for 40 minutes. In UAE, powers of 160, 480, and 792 W were used, ranging time between 2 and 10 minutes at 20 kHz. Agitation extraction (300 rpm) used the same times as UAE and temperature of 72 °C. Soxhlet extraction was carried out for 6 hours. The total phenolic content (TPC) of the extracts was determined by the Folin-Ciocalteu method. The obtained TPCs were, in mg GAE/g sample: PLE (17.65 ± 0.03), UAE (9.95 ± 0.08), Agitation (3.65 ± 0.01), and Soxhlet (2.19 ± 0.05). The highest yield in PLE (110 °C) showed that temperature significantly influenced the extraction, whereas, in UAE, cavitation increased mass transfer and, therefore, the extraction of the target compounds. In general, the TPC of extracts obtained by emerging methods was higher than those obtained by conventional methods, demonstrating the great potential of these techniques to recover bioactive compounds from plant matrices.