Title: Expanding Datasets With Guided Imagination. Abstract: The power of Deep Neural Networks (DNNs) depends heavily on the training data quantity, quality and diversity. However, in many real scenarios, it is costly and time-consuming to collect and annotate large-scale data. This has severely hindered the application of DNNs. To address this challenge, we explore a new task of dataset expansion, which seeks to automatically create new labeled samples to expand a small dataset. To this end, we present a Guided Imagination Framework (GIF)  that leverages the recently developed big generative models (e.g., DALL-E2) to ``imagine'' and create informative new data from seed data to expand small datasets. Specifically, GIF conducts imagination by optimizing the latent features of seed data in a semantically meaningful space, which are fed into the generative models to generate photo-realistic images with new contents. For guiding the imagination towards creating samples useful for model training, we exploit the zero-shot recognition ability of CLIP and introduce three criteria to encourage informative sample generation, i.e., prediction consistency, entropy maximization and diversity promotion.  With these essential criteria as guidance, GIF works well for expanding datasets in different domains,  leading to 29.9\% accuracy gain on average over six natural image datasets, and 10.4\% accuracy gain on average over three medical image datasets. The source code will be made public. 