diff --git a/ql/src/go.qll b/ql/src/go.qll
index b7d8af964a1..d2dc498b6f2 100644
--- a/ql/src/go.qll
+++ b/ql/src/go.qll
@@ -9,6 +9,7 @@ import semmle.go.Concepts
 import semmle.go.Decls
 import semmle.go.Expr
 import semmle.go.Files
+import semmle.go.GoModExpr
 import semmle.go.Locations
 import semmle.go.Packages
 import semmle.go.Scopes
diff --git a/ql/src/semmle/go/AST.qll b/ql/src/semmle/go/AST.qll
index 3d1dddf8981..a58a8c3d78a 100644
--- a/ql/src/semmle/go/AST.qll
+++ b/ql/src/semmle/go/AST.qll
@@ -16,6 +16,7 @@ class AstNode extends @node, Locatable {
    */
   AstNode getChild(int i) {
     result = this.(ExprParent).getChildExpr(i) or
+    result = this.(GoModExprParent).getChildGoModExpr(i) or
     result = this.(StmtParent).getChildStmt(i) or
     result = this.(DeclParent).getDecl(i) or
     result = this.(GenDecl).getSpec(i) or
@@ -70,6 +71,29 @@ class ExprParent extends @exprparent, AstNode {
   int getNumChildExpr() { result = count(getAChildExpr()) }
 }
 
+/**
+ * An AST node whose children include go.mod expressions.
+ */
+class GoModExprParent extends @modexprparent, AstNode {
+  /**
+   * Gets the `i`th child expression of this node.
+   *
+   * Note that the precise indices of child expressions are considered an implementation detail
+   * and are subject to change without notice.
+   */
+  GoModExpr getChildGoModExpr(int i) { modexprs(result, _, this, i) }
+
+  /**
+   * Gets an expression that is a child node of this node in the AST.
+   */
+  GoModExpr getAChildGoModExpr() { result = getChildGoModExpr(_) }
+
+  /**
+   * Gets the number of child expressions of this node.
+   */
+  int getNumChildGoModExpr() { result = count(getAChildGoModExpr()) }
+}
+
 /**
  * An AST node whose children include statements.
  */
diff --git a/ql/src/semmle/go/Files.qll b/ql/src/semmle/go/Files.qll
index 963c9943106..170ba9c2b3d 100644
--- a/ql/src/semmle/go/Files.qll
+++ b/ql/src/semmle/go/Files.qll
@@ -178,7 +178,8 @@ class Folder extends Container, @folder {
 }
 
 /** A file. */
-class File extends Container, @file, Documentable, ExprParent, DeclParent, ScopeNode {
+class File extends Container, @file, Documentable, ExprParent, GoModExprParent, DeclParent,
+  ScopeNode {
   override Location getLocation() { has_location(this, result) }
 
   override string getAbsolutePath() { files(this, result, _, _, _) }
diff --git a/ql/src/semmle/go/GoModExpr.qll b/ql/src/semmle/go/GoModExpr.qll
new file mode 100644
index 00000000000..fced69266f7
--- /dev/null
+++ b/ql/src/semmle/go/GoModExpr.qll
@@ -0,0 +1,167 @@
+/**
+ * Provides classes for working with go.mod expressions.
+ */
+
+import go
+
+/**
+ * A go.mod expression.
+ */
+class GoModExpr extends @modexpr, GoModExprParent {
+  /**
+   * Gets the kind of this expression, which is an integer value representing the expression's
+   * node type.
+   *
+   * Note that the mapping from node types to integer kinds is considered an implementation detail
+   * and subject to change without notice.
+   */
+  int getKind() { modexprs(this, result, _, _) }
+
+  /**
+   * Get the comment group associated with this expression.
+   */
+  DocComment getComments() { result.getDocumentedElement() = this }
+
+  override string toString() { result = "go.mod expression" }
+}
+
+/**
+ *  A top-level block of comments separate from any rule.
+ */
+class GoModCommentBlock extends @modcommentblock, GoModExpr { }
+
+/**
+ * A single line of tokens.
+ */
+class GoModLine extends @modline, GoModExpr {
+  /**
+   * Gets the `i`th token on this line.
+   */
+  string getToken(int i) { modtokens(result, this, i) }
+
+  override string toString() { result = "go.mod line" }
+}
+
+/**
+ * A line that contains the module information
+ */
+class GoModModuleLine extends GoModLine {
+  GoModModuleLine() {
+    this.getParent().(GoModLineBlock).getToken(0) = "module"
+    or
+    not this.getParent() instanceof GoModLineBlock and
+    this.getToken(0) = "module"
+  }
+
+  string getPath() {
+    if this.getParent() instanceof GoModLineBlock
+    then result = this.getToken(1)
+    else result = this.getToken(0)
+  }
+
+  override string toString() { result = "go.mod module line" }
+}
+
+/**
+ * A factored block of lines, for example `require ( "path" )`.
+ */
+class GoModLineBlock extends @modlineblock, GoModExpr {
+  /**
+   * Gets the `i`th token of this line block.
+   */
+  string getToken(int i) { modtokens(result, this, i) }
+
+  override string toString() { result = "go.mod line block" }
+}
+
+/**
+ * A line that declares the Go version to be used, for example `go 1.14`.
+ */
+class GoModGoLine extends GoModLine {
+  GoModGoLine() { this.getToken(0) = "go" }
+
+  /** Gets the Go version declared. */
+  string getVer() { result = this.getToken(1) }
+
+  override string toString() { result = "go.mod go line" }
+}
+
+private string getOffsetToken(GoModLine line, int i) {
+  if line.getParent() instanceof GoModLineBlock
+  then result = line.getToken(i - 1)
+  else result = line.getToken(i)
+}
+
+/**
+ * A line that declares a requirement, for example `require "path"`.
+ */
+class GoModRequireLine extends GoModLine {
+  GoModRequireLine() {
+    this.getParent().(GoModLineBlock).getToken(0) = "require"
+    or
+    not this.getParent() instanceof GoModLineBlock and
+    this.getToken(0) = "require"
+  }
+
+  /** Gets the path of the dependency. */
+  string getPath() { result = getOffsetToken(this, 1) }
+
+  /** Gets the version of the dependency. */
+  string getVer() { result = getOffsetToken(this, 2) }
+
+  override string toString() { result = "go.mod require line" }
+}
+
+/**
+ * A line that declares a dependency version to exclude, for example `exclude "ver"`.
+ */
+class GoModExcludeLine extends GoModLine {
+  GoModExcludeLine() {
+    this.getParent().(GoModLineBlock).getToken(0) = "exclude"
+    or
+    not this.getParent() instanceof GoModLineBlock and
+    this.getToken(0) = "exclude"
+  }
+
+  /** Gets the path of the dependency to exclude a version of. */
+  string getPath() { result = getOffsetToken(this, 1) }
+
+  /** Gets the excluded version. */
+  string getVer() { result = getOffsetToken(this, 2) }
+
+  override string toString() { result = "go.mod exclude line" }
+}
+
+/**
+ * A line that specifies a dependency to use instead of another one, for example
+ * `replace "a" => "b" ver`.
+ */
+class GoModReplaceLine extends GoModLine {
+  GoModReplaceLine() {
+    this.getParent().(GoModLineBlock).getToken(0) = "replace"
+    or
+    not this.getParent() instanceof GoModLineBlock and
+    this.getToken(0) = "replace"
+  }
+
+  /** Gets the path of the dependency to be replaced. */
+  string getOriginalPath() { result = getOffsetToken(this, 1) }
+
+  /** Gets the path of the replacement dependency. */
+  string getReplacementPath() { result = getOffsetToken(this, 3) }
+
+  /** Gets the version of the replacement dependency. */
+  string getReplacementVer() { result = getOffsetToken(this, 4) }
+
+  override string toString() { result = "go.mod replace line" }
+}
+
+/** A left parenthesis for a line block. */
+class GoModLParen extends @modlparen, GoModExpr {
+  override string toString() { result = "go.mod (" }
+}
+
+/** A right parenthesis for a line block. */
+class GoModRParen extends @modrparen, GoModExpr {
+  override string toString() { result = "go.mod )" }
+}