While the value of asset inventory usually goes unchallenged, it is still surprising how few organizations are doing it effectively. World renowned Stuxnet and ICS cybersecurity expert, Ralph Langner discusses the importance of OT/ICS asset inventory, along with the differences between passive scanning and selective probing. Mr. Langner concisely describes what is technically meant by passive scanning, as well as its limitations, including devices and characteristics that will likely not be detected. He concludes the article with an informative look at selective probing, which queries metadata that provides details far more comprehensive than the passive scanning counterpart. Members looking to bolster their comprehensive asset management program are encouraged to consider the benefits of each. Langner.