Although labor trafficking has received much attention in recent years, there is limited empirical research into the depth, breadth, and scope of the problem due to the high costs and methodological challenges associated with these studies. The scarcity of reliable estimates on labor trafficking activities has long been a concern for international organizations and government agencies. Both policy makers and advocacy groups recognize that anti-trafficking campaigns cannot gain credibility without the support of empirical evidence and reliable statistics. Labor trafficking is wide-spread among unauthorized Spanish-speaking migrant workers in San Diego County, with estimates that over 30% of this population are trafficking victims and 55% are victims of abusive labor practices or gross exploitation. The study results include that: 1) the Respondent-Driven Sampling method can be successfully applied to studying labor trafficking activities in well-defined geographical regions with known concentrations of unauthorized immigrant populations. 2) Violations and abuses inflicted by smugglers during transportation were far less common than those inflicted by employers; 6% of those who traveled with smugglers experienced trafficking violations compared to approximately 28% at the workplace while the combined rate of victimization (violations and abusive practices) during transportation was 23% compared to 52% at the workplace. 3) There are marked variations across business sectors with agriculture having the lowest rate and construction and janitorial services have the highest number of violations and abuses. 4) Wage and employment conditions vary tremendously from business to business, the fragmented labor market and diverse job requirements make it easy for unscrupulous employers to take advantage of unauthorized workers.