Granger causality is a fundamental technique for causal inference in time series data, commonly used in the social and biological sciences. Typical operationalizations of Granger causality make a strong assumption that every time point of the e ect time series is in uenced by a combination of other time series with a xed time delay. e assumption of xed time delay also exists in Transfer Entropy, which is considered to be a non-linear version of Granger causality. However, the assumption of the xed time delay does not hold in many applications, such as collective behavior, nancial markets, and many natural phenomena. To address this issue, we develop Variable-lag Granger causality and Variable-lag Transfer Entropy, generalizations of both Granger causality and Transfer Entropy that relax the assumption of the xed time delay and allow causes to in uence e ects with arbitrary time delays. In addition, we propose a method for inferring both variable-lag Granger causality and Transfer Entropy relations. We demonstrate our approaches on an application for studying coordinated collective behavior and other real-world casual-inference datasets and show that our proposed approaches perform be er than several existing methods in both simulated and real-world datasets. Our approaches can be applied in any domain of time series analysis. e so ware of this work is available in the R-CRAN package: VLTimeCausality.