note: Duplication. Profiled as a REST API here: https://www.programmableweb.com/api/salesforce-marketing-cloud, and
SOAP API here: https://www.programmableweb.com/api/salesforce-marketing-cloud-soap
Developers using the Salesforce.com Marketing Cloud API can deploy either its SOAP or REST interface. The SOAP interface is useful for accessing the API’s email functionalities such as tracking, subscriptions, sends, and content. When deploying the SOAP interface, code libraries are used to convert relevant programming languages into SOAP envelopes in turn facilitate data transmission between a user and the Marketing Cloud API. The API’s REST interface is useful for accessing its overall marketing cloud functionalities that include: contacts, content, journey builder, campaigns, and mobile push. The REST interface conveys requests and responses in JSON format. Both the REST and SOAP interfaces of the Marketing Cloud API share the OAuth 2.0 authentication mechanism.