diff --git a/functions.go b/functions.go
new file mode 100644
index 0000000..56f5210
--- /dev/null
+++ b/functions.go
@@ -0,0 +1,108 @@
+package sets
+
+// Union returns a union of the given sets (left ∪ right)
+func Union[T comparable](left, right *Set[T]) *Set[T] {
+	left.mux.RLock()
+	right.mux.RLock()
+	defer left.mux.RUnlock()
+	defer right.mux.RUnlock()
+
+	store := map[T]struct{}{}
+
+	for k := range left.store {
+		store[k] = struct{}{}
+	}
+	for k := range right.store {
+		if _, ok := store[k]; !ok {
+			store[k] = struct{}{}
+		}
+	}
+
+	return &Set[T]{
+		store: store,
+	}
+}
+
+// Intersection returns an intersection of the given sets (left ∩ right)
+func Intersection[T comparable](left, right *Set[T]) *Set[T] {
+	left.mux.RLock()
+	right.mux.RLock()
+	defer left.mux.RUnlock()
+	defer right.mux.RUnlock()
+
+	store := map[T]struct{}{}
+
+	for lk := range left.store {
+		if _, ok := right.store[lk]; ok {
+			store[lk] = struct{}{}
+		}
+	}
+
+	return &Set[T]{
+		store: store,
+	}
+}
+
+// Diff returns the relative complement of sets (left ∖ right)
+func Diff[T comparable](left, right *Set[T]) *Set[T] {
+	left.mux.RLock()
+	right.mux.RLock()
+	defer left.mux.RUnlock()
+	defer right.mux.RUnlock()
+
+	store := map[T]struct{}{}
+
+	for lk := range left.store {
+		if _, ok := right.store[lk]; !ok {
+			store[lk] = struct{}{}
+		}
+	}
+
+	return &Set[T]{
+		store: store,
+	}
+}
+
+// SymmetricDiff returns the symmetric difference between sets (left ⊖ right)
+func SymmetricDiff[T comparable](left, right *Set[T]) *Set[T] {
+	left.mux.RLock()
+	right.mux.RLock()
+	defer left.mux.RUnlock()
+	defer right.mux.RUnlock()
+
+	store := map[T]struct{}{}
+
+	for lk := range left.store {
+		if _, ok := right.store[lk]; !ok {
+			store[lk] = struct{}{}
+		}
+	}
+	for rk := range right.store {
+		if _, ok := left.store[rk]; !ok {
+			store[rk] = struct{}{}
+		}
+	}
+
+	return &Set[T]{
+		store: store,
+	}
+}
+
+// Equal checks whether the sets are equal (left = right)
+func Equal[T comparable](left, right *Set[T]) bool {
+	left.mux.RLock()
+	right.mux.RLock()
+	defer left.mux.RUnlock()
+	defer right.mux.RUnlock()
+
+	if len(left.store) != len(right.store) {
+		return false
+	}
+
+	for lk := range left.store {
+		if _, ok := right.store[lk]; !ok {
+			return false
+		}
+	}
+	return true
+}
diff --git a/functions_test.go b/functions_test.go
new file mode 100644
index 0000000..1149f7e
--- /dev/null
+++ b/functions_test.go
@@ -0,0 +1,61 @@
+package sets
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func getSetForElements(t *testing.T, elements ...int) *Set[int] {
+	t.Helper()
+
+	target := map[int]struct{}{}
+	for _, el := range elements {
+		target[el] = struct{}{}
+	}
+
+	return &Set[int]{
+		store: target,
+	}
+}
+
+func TestUnion(t *testing.T) {
+	base := getSetForElements(t, 0, 1, 2, 3, 4, 5)
+	other := getSetForElements(t, 3, 4, 5, 6, 7, 8)
+	expected := []int{0, 1, 2, 3, 4, 5, 6, 7, 8}
+
+	require.ElementsMatch(t, expected, Union(base, other).Slice())
+}
+
+func TestIntersection(t *testing.T) {
+	base := getSetForElements(t, 0, 1, 2, 3, 4, 5)
+	other := getSetForElements(t, 3, 4, 5, 6, 7, 8)
+	expected := []int{3, 4, 5}
+
+	require.ElementsMatch(t, expected, Intersection(base, other).Slice())
+}
+
+func TestDiff(t *testing.T) {
+	base := getSetForElements(t, 0, 1, 2, 3, 4, 5)
+	other := getSetForElements(t, 3, 4, 5, 6, 7, 8)
+	expected := []int{0, 1, 2}
+
+	require.ElementsMatch(t, expected, Diff(base, other).Slice())
+}
+
+func TestSymmetricDiff(t *testing.T) {
+	base := getSetForElements(t, 0, 1, 2, 3, 4, 5)
+	other := getSetForElements(t, 3, 4, 5, 6, 7, 8)
+	expected := []int{0, 1, 2, 6, 7, 8}
+
+	require.ElementsMatch(t, expected, SymmetricDiff(base, other).Slice())
+}
+
+func TestEqual(t *testing.T) {
+	base := getSetForElements(t, 0, 1, 2, 3, 4, 5)
+	otherDifferent := getSetForElements(t, 3, 4, 5, 6, 7, 8)
+	otherEqual := getSetForElements(t, 0, 1, 2, 3, 4, 5)
+
+	require.False(t, Equal(base, otherDifferent))
+	require.True(t, Equal(base, otherEqual))
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..eeea02f
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,11 @@
+module pkg.icikowski.pl/sets
+
+go 1.20
+
+require github.com/stretchr/testify v1.8.4
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..fa4b6e6
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,10 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=
+github.com/stretchr/testify v1.8.4/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXlSw2iwfAo=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/package.go b/package.go
new file mode 100644
index 0000000..96fabac
--- /dev/null
+++ b/package.go
@@ -0,0 +1,4 @@
+/*
+Sets-related types & functions
+*/
+package sets
diff --git a/set.go b/set.go
new file mode 100644
index 0000000..ae88d37
--- /dev/null
+++ b/set.go
@@ -0,0 +1,77 @@
+package sets
+
+import (
+	"sync"
+)
+
+// Set represents a set of values
+type Set[T comparable] struct {
+	store map[T]struct{}
+	mux   sync.RWMutex
+}
+
+// New creates a new set
+func New[T comparable](data ...T) *Set[T] {
+	set := &Set[T]{
+		store: map[T]struct{}{},
+	}
+
+	for _, element := range data {
+		set.Insert(element)
+	}
+	return set
+}
+
+// Size returns number of elements in set
+func (s *Set[T]) Size() int {
+	s.mux.RLock()
+	defer s.mux.RUnlock()
+
+	return len(s.store)
+}
+
+// Contains checks whether the value is contained in the set
+func (s *Set[T]) Contains(val T) bool {
+	s.mux.RLock()
+	defer s.mux.RUnlock()
+
+	_, ok := s.store[val]
+	return ok
+}
+
+// Insert inserts a value into the set if the value was not already present
+func (s *Set[T]) Insert(val T) bool {
+	s.mux.Lock()
+	defer s.mux.Unlock()
+
+	if _, ok := s.store[val]; !ok {
+		s.store[val] = struct{}{}
+		return false
+	}
+	return true
+}
+
+// Delete removes a value from the set if the value was already present
+func (s *Set[T]) Delete(val T) bool {
+	s.mux.Lock()
+	defer s.mux.Unlock()
+
+	if _, ok := s.store[val]; ok {
+		delete(s.store, val)
+		return true
+	}
+	return false
+}
+
+// Slice returns a slice which contains the elements from the set
+func (s *Set[T]) Slice() []T {
+	s.mux.RLock()
+	defer s.mux.RUnlock()
+
+	elements := []T{}
+	for k := range s.store {
+		elements = append(elements, k)
+	}
+
+	return elements
+}
diff --git a/set_test.go b/set_test.go
new file mode 100644
index 0000000..3792e43
--- /dev/null
+++ b/set_test.go
@@ -0,0 +1,61 @@
+package sets
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func getTestSet(t *testing.T) *Set[int] {
+	t.Helper()
+
+	return &Set[int]{
+		store: map[int]struct{}{
+			0: {},
+			1: {},
+			2: {},
+			3: {},
+			4: {},
+			5: {},
+			6: {},
+			7: {},
+			8: {},
+			9: {},
+		},
+	}
+}
+
+func TestSetSize(t *testing.T) {
+	s := getTestSet(t)
+
+	require.Equal(t, 10, s.Size())
+}
+
+func TestSetContains(t *testing.T) {
+	s := getTestSet(t)
+
+	require.True(t, s.Contains(0))
+	require.False(t, s.Contains(10))
+}
+
+func TestSetInsert(t *testing.T) {
+	s := getTestSet(t)
+
+	require.True(t, s.Insert(0))
+	require.False(t, s.Insert(10))
+	require.Contains(t, s.store, 10)
+}
+
+func TestSetDelete(t *testing.T) {
+	s := getTestSet(t)
+
+	require.False(t, s.Delete(10))
+	require.True(t, s.Delete(0))
+	require.NotContains(t, s.store, 0)
+}
+
+func TestSetSlice(t *testing.T) {
+	s := getTestSet(t)
+
+	require.ElementsMatch(t, []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}, s.Slice())
+}