Project Based Learning (PjBL) has emerged as a promising approach in mathematics education. This study aims to analyze the implementation of project-based learning (PjBL) internationally in mathematics education and to identify the underlying learning theories, such as the method of writing an article through SLR. A systematic literature review uses the "Publish or Perish" application for Scopus and Crossref searches. The selection criteria include accredited journal articles from Sinta 1, Sinta 2, or those already accredited by Scopus from 2014 to 2024 in English, focusing on mathematics/mathematics education. Out of the ten selected articles, further analysis was conducted. PjBL effectively enhances academic achievement. 21st-century skills include critical thinking, problem-solving, collaboration, communication, creativity, technological literacy, and student motivation in mathematics education across various countries. Implementing the PjBL model in mathematics involves a series of well-defined steps: presenting problems, preparing project plans and schedules, forming effective teams, providing support, integrating with the curriculum, using visual media, presenting and evaluating results, and reflecting on the process. The implementation challenges include inflexible schedules and teachers' need for more professional skills. The theories underlying the effectiveness of PjBL include constructivism, social learning, experiential learning, multiple intelligences, contextual learning, motivation, and problem-solving. PjBL shows significant potential in enhancing international mathematics learning. Implementation success depends on thorough preparation, appropriate support, and adjustments to the local context. Further research is needed to optimize the integration of PjBL with traditional methods, address implementation challenges, and analyze its long-term impacts.