All About Tabular Model Relationships

Understand star schema and the importance for Power BI {PBI docs}

Model relationships in Power BI Desktop {PBI docs}

Back to Basics: Power BI Relationship Demystified {RADACAD}

Bi-directional relationship guidance {PBI docs}

One-to-one relationship guidance {PBI docs}

Many-to-many relationship guidance {PBI docs}

Active vs inactive relationship guidance {PBI docs}

Bidirectional relationships and ambiguity in DAX {SQLBI}

Killing me softly…Bi-directional relationships in Power BI {Nikola Ilic at Data Mozart}

Power Pivot Principles: Ambiguity of Bidirectional Relationships in Power BI {SumProduct}

Building a Virtual Relationship in Power BI – Basics of TREATAS DAX Function {RADACAD}

Best Practices to Handle Multiple Fact Tables in Power BI by Nuric Ugarte at DataMartin

Expanded tables in DAX {SQLBI}
“…table expansion as the vital concept required to understand why DAX behaves a certain way”

Relationship troubleshooting guidance {PBI docs}