Background/Objectives: Internet addiction (IA) and related behaviors, such as Internet Gaming Disorder (IGD) and social media addiction (SMA), have gained increasing research attention. Studies show gender differences, with males more likely to develop gaming-related addictions and females more prone to social media and phubbing behaviors. This study aimed to explore gender differences in Internet addiction and related behaviors in a Spanish sample, with the goal of identifying predictors and gender-specific patterns of IA. Methods: We conducted a cross-sectional study with 585 participants (265 male, 320 female) aged 18 to 35 years (M = 22.11, SD = 3.08). Data were collected using standardized questionnaires to assess IA, IGD, SMA, phubbing, Fear of Missing Out (FoMO), emotional dysregulation, personality traits, and prosociality. Correlation and regression analyses were used to identify gender-specific predictors of IA. Results: Males exhibited significantly higher scores for IA and IGD, while females showed higher scores for SMA and the “phone obsession” dimension of phubbing. No significant gender differences were found in the “communication disturbance” dimension of phubbing or in FoMO. Correlation analyses revealed significant associations between IA and psychological as well as technological variables. Gender-specific predictors of IA included social media engagement and emotional regulation for females, while gaming behaviors and communication patterns were more relevant for males. Conclusions: These findings highlight gender differences in IA, suggesting that tailored interventions should address unique online behaviors and emotional regulation challenges in males and females. Future research should refine gender-specific patterns to develop more effective, targeted prevention and treatment strategies.