Import/export procedures can be simple, or it can be mindbogglingly complicated, requiring up to 5 individual permits/certificates for a given shipment. The details all depend on a number of different factors.
I suggest avoiding going into this venture unless you are dead serious about doing everything correctly. Also, while not always the case, as others have said, sometimes it’s not worth the effort because many international imports arrive in poor condition.
So, in any case, for the sake of information:
There are two sides to the process. The Export and the Import. For a shipment to be legal, the originating nursery needs to follow Export law in the originating country, and you need to follow Import law in the destination country. Since you are in the US, I’ll limit this to just for exportation from a foreign country for import into the US. Other countries may have even more complicated rules.
The following are various factors that may change the import/export procedures:
CITES status of the species (Appendix I or II) - All orchids are at least Appendix II, with a bunch listed explicitly in Appendix I. The requirements for export and import are different between the two Appendices, but all orchids will require at least a CITES export permit from the originating country.
Endangerd Species Act Status - Is the species specially covered by the Endangered species act in addition to CITES? If so, it may require an additional permit.
Flasks or loose plants - The import procedures and paperwork required is different for flasks than they are for loose plants. The only practical way to import certain species (i.e. Appendix I) is in a flask. Loose plants must be bare root and clean or potted in an approved medium if coming from an approved facility.
The country you are importing from - Each country has their own export laws and paperwork required to allow the plants to even leave their borders. The US also has different regulations for certain exporting countries.
How many plants you are importing - The exporting country may have legal requirements pertaining to the number of plants you are exporting. The US has different procedures depending on how many plants you have in the shipment.
Quantity of each cultivar you are importing - The exporting country may have restrictions on the numbers of each cultivar in a shipment, and the US sometimes has different procedures depending on the number of individuals of the same cultivar.
What state you are importing to in the US - Some states have stricter importation laws than the federal law, and may require additional permits and inspections.
Intent to sell the imported plants - Importation for intent to sell requires formal importation procedures and full import permits regardless of quantity of plants. Importation of 12 or fewer individual plants for personal use may waive the need to obtain the permit if other requirements are also met.
Possible requirements for export out of the originating country:
Cites Export Permit for each species - The exporter needs to go to their governmental agriculture office to obtain a CITES export permit for the individual shipment. Each shipment requires its own permit. The office may subject the nursery for inspection to ensure that CITES regulations in regards to propagation are met. The exporter will usually have you reimburse them for the fees.
Cites Import Permit information of the importer in the destination country - Some countries require that the importer (you) have a permit regardless of the US law to even allow the plants out of their borders.
Phytosanitary certificate - The exporter needs to go to the ag office to have the plants inspected and get a phytosanitary certificate. The nursery may also need to subject their facilities for inspection for sanitary conditions. They’ll usually have you reimburse them for these fees as well.
Possible requirements for importation into the US:
Cites Export Permit from originating country for each species - The original signed export permit for each species (or one listing out multiple species) needs to be affixed to the package.
Phytosanitary certificate - The original signed phytosanitary certificate from the originating country needs to be affixed to the package
Customs form - The customs form from the originating country needs to list the correct species and quantity of plants.
Purchase Invoice - The purchase invoice will need to be affixed to the package.
Protected Species Import Permit from the US for each species if required - Always required for CITES Appendix I species, and may be required for other species protected by the Endangered Species Act.
Agricultural Import Permit from the USDA for each species - Depending on certain specifics you may have to register with the USDA and obtain an import permit to import the plants.
State import permit from the destination state - If required by your resident state
USDA inspection and quarantine center shipping labels - If you are required an import permit for a given shipment, the package cannot be shipped directly to you. The package must be shipped to one of the US Inspection and Quarantine centers, where they will inspect the plants and treat or quarantine as necessary. They will then contact you and ship to you after the plants have cleared.
Plants individually and clearly labeled inside the package - For the purpose of identification during inspections.
Shipping considerations:
If you are not required a USDA import permit for a given shipment, the package may be shipped directly to you. However, if your shipment requires a USDA import permit, the package must be shipped to a quarantine and inspection center. When you sign up for an import permit, USDA office will send you green/yellow shipping labels. These must be physically sent to the exporter, and the exporter must affix this to the package. The package is then delivered directly to the inspection/quarantine center, they inspect it, and then forward the package to you once cleared.
Also, some countries have fast international shipping. For example, when I import Neofinetia from Korea, the package usually arrives in 4 days or sooner from the date of shipment. However, some countries do not have reliable shipping services, and sometimes it will take over a month for the package to arrive at your doorstep. While some species are durable enough to withstand that amount of time bareroot and without water, many others cannot.
To complicate this further, if the inspection center finds your plants infected or infested they may retain them for treatment or quarantine (and of course charge you the treatment fees). The quarantine center doesn't necessarily know how to care for the plants properly, so they may sometimes take a beating.
Costs:
The costs of importing legally will vary depending on the specifics listed above, and you'll be paying separate fees to a number of places rather than as a single lump sum. However, the sum of the fees you may end up paying range from a minimum of $100 upwards of $500+ for each shipment.
Violation of the Law:
For Appendix II species, violation of any law or procedure in the importation process will usually end up in the USDA contacting you to correct the violations or sign up for any missing paperwork. If you cannot correct the violations or if the package is missing a CITES export permit or a Phytosanitary certificate from the originating country, the shipment is either returned to the sender, confiscated or destroyed.
For Appendix I species, violation of the CITES laws is a serious matter and may involve prosecution with possible jail time and enormous fines.