Title: Hierarchical Image-to-image Translation with Nested Distributions Modeling. Abstract: Unpaired image-to-image translation among category domains has achieved remarkable success in past decades. Recent studies mainly focus on two challenges. For one thing, such translation is inherently multimodal due to variations of domain-specific information (e.g., the domain of house cat has multiple fine-grained subcategories). For another, existing multimodal approaches have limitations in handling more than two domains, i.e. they have to independently build one model for every pair of domains. To address these problems, we propose the Hierarchical Image-to-image Translation (HIT) method which jointly formulates the multimodal and multi-domain problem in a semantic hierarchy structure, and can further control the uncertainty of multimodal. Specifically, we regard the domain-specific variations as the result of the multi-granularity property of domains, and one can control the granularity of the multimodal translation by dividing a domain with large variations into multiple subdomains which capture local and fine-grained variations. With the assumption of Gaussian prior, variations of domains are modeled in a common space such that translations can further be done among multiple domains within one model. To learn such complicated space, we propose to leverage the inclusion relation among domains to constrain distributions of parent and children to be nested. Experiments on several datasets validate the promising results and competitive performance against state-of-the-arts.