The broad autism phenotype is the phenotypic expression of the primary characteristics of autism. However, currently available tests do not agree with the two-domain operationalization of broad autism phenotype or autism, and their internal structure has shown instability across applications. This study presents the Broad Autism Phenotype--International Test, the first such test designed to target a two-domain operationalization in Spain and the United Kingdom. A broad pilot study was conducted in three community samples, two from Spain (ES1, N = 970; ES2, N = 460) and one from the United Kingdom (N = 530). The Broad Autism Phenotype--International Test consists of 20 items distributed into the SOCIAL-BAP and RIRE-BAP dimensions, representing the seven autistic subdomains. Common factor approaches were used to find a simple and invariant factor structure between countries. The Broad Autism Phenotype--International Test presents full metric invariance between two Spanish samples, partial invariance between countries, and adequate omega reliability estimation. Evidence-based results on the relationships of the SOCIAL-BAP and RIRE-BAP to other variables (the Social Responsiveness Scale-2 and the Broad Autism Phenotype Questionnaire) support the interpretation of its scores for the intended uses. The evidence provided in this article shows that the Broad Autism Phenotype--International Test functions adequately compared to other available broad autism phenotype tests, such as the Broad Autism Phenotype Questionnaire.