diff --git a/BUILD.yaml b/BUILD.yaml
index c0cdd95..6d727de 100644
--- a/BUILD.yaml
+++ b/BUILD.yaml
@@ -17,6 +17,7 @@ packages:
       - go.sum
     deps:
       - :helloworld
+      - :doesntExist?
     argdeps:
       - version
     prep:
diff --git a/README.md b/README.md
index 1c093fe..6a779ed 100644
--- a/README.md
+++ b/README.md
@@ -67,6 +67,7 @@ description: A sentence describing what the script is good for.
 # contains tools you want to use in a script.
 deps:
 - some/other:package
+- some/other:optional?
 # Env sets environment variables which are present during script execution.
 env:
 - MESSAGE=hello
diff --git a/pkg/leeway/package.go b/pkg/leeway/package.go
index bb6b8c4..865013c 100644
--- a/pkg/leeway/package.go
+++ b/pkg/leeway/package.go
@@ -124,7 +124,7 @@ func (c *Component) Git() *GitInfo {
 
 // PackageNotFoundErr is used when something references a package we don't know about
 type PackageNotFoundErr struct {
-	Package string
+	Package PackageDependency
 }
 
 func (n PackageNotFoundErr) Error() string {
@@ -132,15 +132,59 @@ func (n PackageNotFoundErr) Error() string {
 }
 
 type packageInternal struct {
-	Name                 string            `yaml:"name"`
-	Type                 PackageType       `yaml:"type"`
-	Sources              []string          `yaml:"srcs"`
-	Dependencies         []string          `yaml:"deps"`
-	Layout               map[string]string `yaml:"layout"`
-	ArgumentDependencies []string          `yaml:"argdeps"`
-	Environment          []string          `yaml:"env"`
-	Ephemeral            bool              `yaml:"ephemeral"`
-	PreparationCommands  [][]string        `yaml:"prep"`
+	Name                 string              `yaml:"name"`
+	Type                 PackageType         `yaml:"type"`
+	Sources              []string            `yaml:"srcs"`
+	Dependencies         []PackageDependency `yaml:"deps"`
+	Layout               map[string]string   `yaml:"layout"`
+	ArgumentDependencies []string            `yaml:"argdeps"`
+	Environment          []string            `yaml:"env"`
+	Ephemeral            bool                `yaml:"ephemeral"`
+	PreparationCommands  [][]string          `yaml:"prep"`
+}
+
+type PackageDependency string
+
+func (dep PackageDependency) Valid() bool {
+	_, pkg := dep.segs()
+	return pkg != ""
+}
+
+func (dep PackageDependency) segs() (comp, pkg string) {
+	segs := strings.Split(dep.FullPackage(), ":")
+	if len(segs) != 2 {
+		return
+	}
+	return segs[0], segs[1]
+}
+
+// Component returns the component of the depdency
+func (dep PackageDependency) Component() string {
+	comp, _ := dep.segs()
+	return comp
+}
+
+// FullPackage returns the name of the package this dependency refers to
+func (dep PackageDependency) FullPackage() string {
+	return strings.TrimSuffix(string(dep), "?")
+}
+
+// Optional returns true if the dependency is optional
+func (dep PackageDependency) Optional() bool {
+	return strings.HasSuffix(string(dep), "?")
+}
+
+// Relative returns true if the dependency is relative within its component
+func (dep PackageDependency) Relative() bool {
+	return strings.HasPrefix(string(dep), ":")
+}
+
+func (dep PackageDependency) WithComponent(comp string) PackageDependency {
+	_, pkg := dep.segs()
+	if dep.Optional() {
+		pkg += "?"
+	}
+	return PackageDependency(comp + ":" + pkg)
 }
 
 // Package is a single buildable artifact within a component
@@ -168,17 +212,20 @@ func (p *Package) link(idx map[string]*Package) error {
 		return nil
 	}
 
-	p.dependencies = make([]*Package, len(p.Dependencies))
+	p.dependencies = make([]*Package, 0, len(p.Dependencies))
 	p.layout = make(map[*Package]string)
-	for i, dep := range p.Dependencies {
-		deppkg, ok := idx[dep]
+	for _, dep := range p.Dependencies {
+		deppkg, ok := idx[dep.FullPackage()]
 		if !ok {
+			if dep.Optional() {
+				continue
+			}
 			return PackageNotFoundErr{dep}
 		}
-		p.dependencies[i] = deppkg
+		p.dependencies = append(p.dependencies, deppkg)
 
 		// if the user hasn't specified a layout, tie it down at this point
-		p.layout[deppkg], ok = p.Layout[dep]
+		p.layout[deppkg], ok = p.Layout[dep.FullPackage()]
 		if !ok {
 			p.layout[deppkg] = deppkg.FilesystemSafeName()
 		}
diff --git a/pkg/leeway/package_test.go b/pkg/leeway/package_test.go
index e1953ea..41253fd 100644
--- a/pkg/leeway/package_test.go
+++ b/pkg/leeway/package_test.go
@@ -6,6 +6,108 @@ import (
 	"testing"
 )
 
+func TestPackageDependencyValid(t *testing.T) {
+	tests := []struct {
+		Input       string
+		Expectation bool
+	}{
+		{":foo", true},
+		{":foo?", true},
+		{"absolute/component:foo?", true},
+		{"missing/package", false},
+		{":", false},
+		{"", false},
+	}
+	for _, test := range tests {
+		t.Run(test.Input, func(t *testing.T) {
+			act := PackageDependency(test.Input).Valid()
+			if act != test.Expectation {
+				t.Fatalf("expected %v, got %v", test.Expectation, act)
+			}
+		})
+	}
+}
+
+func TestPackageDependencyOptional(t *testing.T) {
+	tests := []struct {
+		Input       string
+		Expectation bool
+	}{
+		{":foo", false},
+		{":foo?", true},
+		{"absolute/component:foo", false},
+		{"absolute/component:foo?", true},
+	}
+	for _, test := range tests {
+		t.Run(test.Input, func(t *testing.T) {
+			act := PackageDependency(test.Input).Optional()
+			if act != test.Expectation {
+				t.Fatalf("expected %v, got %v", test.Expectation, act)
+			}
+		})
+	}
+}
+
+func TestPackageDependencyRelative(t *testing.T) {
+	tests := []struct {
+		Input       string
+		Expectation bool
+	}{
+		{":foo", true},
+		{":foo?", true},
+		{"absolute/component:foo", false},
+		{"absolute/component:foo?", false},
+	}
+	for _, test := range tests {
+		t.Run(test.Input, func(t *testing.T) {
+			act := PackageDependency(test.Input).Relative()
+			if act != test.Expectation {
+				t.Fatalf("expected %v, got %v", test.Expectation, act)
+			}
+		})
+	}
+}
+
+func TestPackageDependencyComponent(t *testing.T) {
+	tests := []struct {
+		Input       string
+		Expectation string
+	}{
+		{":foo", ""},
+		{":foo?", ""},
+		{"absolute/component:foo?", "absolute/component"},
+		{"", ""},
+	}
+	for _, test := range tests {
+		t.Run(test.Input, func(t *testing.T) {
+			act := PackageDependency(test.Input).Component()
+			if act != test.Expectation {
+				t.Fatalf("expected %v, got %v", test.Expectation, act)
+			}
+		})
+	}
+}
+
+func TestPackageDependencyFullPackage(t *testing.T) {
+	tests := []struct {
+		Input       string
+		Expectation string
+	}{
+		{":foo", ":foo"},
+		{":foo?", ":foo"},
+		{"absolute/component:foo?", "absolute/component:foo"},
+		{"", ""},
+	}
+	for _, test := range tests {
+		t.Run(test.Input, func(t *testing.T) {
+			act := PackageDependency(test.Input).FullPackage()
+			if act != test.Expectation {
+				t.Fatalf("expected %v, got %v", test.Expectation, act)
+			}
+		})
+	}
+}
+
 func TestResolveBuiltinVariables(t *testing.T) {
 	tests := []struct {
 		PkgType     PackageType
diff --git a/pkg/leeway/scripts.go b/pkg/leeway/scripts.go
index 9d8c780..f35dc56 100644
--- a/pkg/leeway/scripts.go
+++ b/pkg/leeway/scripts.go
@@ -37,13 +37,13 @@ const (
 type Script struct {
 	C *Component
 
-	Name          string        `yaml:"name"`
-	Description   string        `yaml:"description"`
-	Dependencies  []string      `yaml:"deps"`
-	Environment   []string      `yaml:"env"`
-	WorkdirLayout WorkdirLayout `yaml:"workdir"`
-	Type          ScriptType    `yaml:"type"`
-	Script        string        `yaml:"script"`
+	Name          string              `yaml:"name"`
+	Description   string              `yaml:"description"`
+	Dependencies  []PackageDependency `yaml:"deps"`
+	Environment   []string            `yaml:"env"`
+	WorkdirLayout WorkdirLayout       `yaml:"workdir"`
+	Type          ScriptType          `yaml:"type"`
+	Script        string              `yaml:"script"`
 
 	dependencies []*Package
 }
@@ -55,13 +55,16 @@ func (p *Script) FullName() string {
 
 // link connects resolves the references to the dependencies
 func (p *Script) link(idx map[string]*Package) error {
-	p.dependencies = make([]*Package, len(p.Dependencies))
-	for i, dep := range p.Dependencies {
-		var ok bool
-		p.dependencies[i], ok = idx[dep]
+	p.dependencies = make([]*Package, 0, len(p.Dependencies))
+	for _, dep := range p.Dependencies {
+		pkg, ok := idx[dep.FullPackage()]
 		if !ok {
+			if dep.Optional() {
+				continue
+			}
 			return PackageNotFoundErr{dep}
 		}
+		p.dependencies = append(p.dependencies, pkg)
 	}
 	return nil
 }
diff --git a/pkg/leeway/workspace.go b/pkg/leeway/workspace.go
index a8a5746..00d3bc3 100644
--- a/pkg/leeway/workspace.go
+++ b/pkg/leeway/workspace.go
@@ -573,12 +573,12 @@ func filterExcludedComponents(variant *PackageVariant, c *Component) (ignoreComp
 
 	for _, p := range c.Packages {
 		for i, dep := range p.Dependencies {
-			segs := strings.Split(dep, ":")
-			if len(segs) != 2 {
+			comp := dep.Component()
+			if comp == "" {
 				continue
 			}
 
-			if variant.ExcludeComponent(segs[0]) {
+			if variant.ExcludeComponent(comp) {
 				p.Dependencies[i] = p.Dependencies[len(p.Dependencies)-1]
 				p.Dependencies = p.Dependencies[:len(p.Dependencies)-1]
 			}
@@ -759,11 +759,11 @@ func loadComponent(ctx context.Context, workspace *Workspace, path string, args
 
 		// make all dependencies fully qualified
 		for idx, dep := range pkg.Dependencies {
-			if !strings.HasPrefix(dep, ":") {
+			if !dep.Relative() {
 				continue
 			}
 
-			pkg.Dependencies[idx] = comp.Name + dep
+			pkg.Dependencies[idx] = dep.WithComponent(comp.Name)
 		}
 		// make all layout entries full qualified
 		if pkg.Layout == nil {
@@ -807,11 +807,11 @@ func loadComponent(ctx context.Context, workspace *Workspace, path string, args
 
 		// make all dependencies fully qualified
 		for idx, dep := range scr.Dependencies {
-			if !strings.HasPrefix(dep, ":") {
+			if !dep.Relative() {
 				continue
 			}
 
-			scr.Dependencies[idx] = comp.Name + dep
+			scr.Dependencies[idx] = dep.WithComponent(comp.Name)
 		}
 	}