Electronic communications devices that operate in environments with a high level of electromagnetic noise require special consideration and testing to ensure the continuous delivery of uncorrupted data. Communication devices are susceptible to data interruption and corruption in industrial, automotive, telecommunication, medical and test lab environments, to name just a few. Demonstrating compliance with international immunity testing standards helps to ensure robust communications in noisy electromagnetic environments. This article provides key recommendations for implementing serial communication systems that exceed Electro-technical Commission (IEC) immunity test standards. To provide an example of highly reliable serial communications system implementation and testing, National Semiconductor’s DP83640 Ethernet physical layer device was tested for IEC immunity test compliance. Results from these tests are included for reference. The scope of this article is restricted to communication signals; immunity issues related to AC and DC power supply signals are not included.