Title: LUNA: Language as Continuing Anchors for Referring Expression Comprehension. Abstract: Referring expression comprehension aims to localize the description of a natural language expression in an image. Using location priors to remedy inaccuracies in cross-modal alignments is the state of the art for CNN-based methods tackling this problem. Recent Transformer-based models cast aside this idea making the case for steering away from hand-designed components. In this work, we propose LUNA, which uses language as continuing anchors to guide box prediction in a Transformer decoder, and show that language-guided location priors can be effectively exploited in a Transformer-based architecture. Specifically, we first initialize an anchor box from the input expression via a small “proto-decoder”, and then use this anchor as location prior in a modified Transformer decoder for predicting the bounding box. Iterating through each decoder layer, the anchor box is first used as a query for pooling multi-modal context, and then updated based on pooled context. This approach allows the decoder to focus selectively on one part of the scene at a time, which reduces noise in multi-modal context and leads to more accurate box predictions. Our method outperforms existing state-of-the-art methods on the challenging datasets of ReferIt Game, RefCOCO/+/g, and Flickr30K Entities.