This project entry contains data files for the paper ‘Instantaneous conventions: The emergence of flexible communicative signals.’ Authored by Jennifer Misyak, Takao Noguchi, and Nick Chater; and accepted to Psychological Science, at time of posting. The Codebook contains a description of the raw and processed variables, as well as labels and composition of trial-types, across all files. Raw data collected for experiments is contained in the “raw_data_expt*” files under the relevant experimental heading. (Timestamps related to variables have European date format, GMT / BST.) In raw data for Expt. 2, please note that files for the Receivers condition also incorporate information from the separately-conducted Senders condition. Participants in the Sender condition have consistent IDs below the 20’s (i.e., from 1 - 16), and participants in the Receivers condition have consistent IDs above the 20’s (i.e., from 21 - 36). For the practice trials, participants within either condition would have received practice in both roles (Sender and Receiver); hence, for practice trials, the same participant ID number will have entries for both “sender” and “interpreter” variables. Processed data files also include worksheets (“individual * data”, “indiv * proportion”) that display count and proportion data for the categorised actions of each participant, by role and per trial-type. (*n.b.* For Expt. 1, cells in the processed data worksheets contain both active formulae and values.)