Ports and harbors are facing stiff competition for market share and delivering more effective and secure flow of goods worldwide. High-performing ports are implementing smart technologies to better manage operations meeting new challenges in maintaining safe, secure, and energy efficient facilities that mitigate environmental impacts. In this context, a new concept has emerged which is called smart port. However, a unified definition of a smart port has not been well documented. This article attempts to develop a framework for a smart port and a quantitative metric, smart port index (SPI), that ports can use to improve their resiliency and sustainability. Our proposed SPI is based on key performance indicators (KPIs) gathered from the literature. These KPIs are organized around four key activity domains of a smart port: operations, environment, energy, and safety & security. Case studies are conducted to show how one can use SPI and to assess the performance of some of the busiest ports in the world. Our methodology provides a quantitative tool for port authorities to develop their smart port strategies, assess their smartness, and identify strengths and weaknesses of their current operations for continuous improvement. Our study reveals that smart port initiatives around the world have different levels of comprehensiveness. The results of this study also suggest that government policies and region-specific variables can impact SPI value.