A number of the frequency bands allocated to amateur radio operators by the FCC are dedicated only to us. But we must share several other bands, or segments of bands, with other services. In all cases where hams share frequencies with others, we hams have Secondary Status.
Per the FCC, "A station in a secondary service must not cause harmful interference to, and must accept interference from, stations in a primary service." (47CFR97.303)
The primary/secondary status of our allocations are officially detailed in the FCC regulations, Sections 301 and 303 (47CFR97.301 & 47CFR97.303). Sorting out just what frequencies are shared, and who they are shared with, is not straightforward. Below is a effort to simplify and summarize the primary/secondary status of each amateur band.
Since the great majority of FCC-authorized hams are in the continental United Status, Alaska or Hawaii (i.e., ITU Region 2), that region has been highlighted on the below spreadsheet. Also, limitations with our website provider mean that you will likely need to scroll horizontally as well as vertically to see the entire spreadsheet. For that reason, the spreadsheet is also available as a downloadable PDF, by clicking this Secondary Status link.