diff --git a/api/tasks/pool.go b/api/tasks/pool.go
index 19c38a8a..60f6ea6e 100644
--- a/api/tasks/pool.go
+++ b/api/tasks/pool.go
@@ -3,49 +3,118 @@ package tasks
 import (
 	"fmt"
 	"time"
+
+	"github.com/ansible-semaphore/semaphore/util"
 )
 
 type taskPool struct {
-	queue    []*task
-	register chan *task
-	running  *task
+	queue       []*task
+	register    chan *task
+	activeProj  map[int]*task
+	activeNodes map[string]*task
+	running     int
 }
 
 var pool = taskPool{
-	queue:    make([]*task, 0),
-	register: make(chan *task),
-	running:  nil,
+	queue:       make([]*task, 0),
+	register:    make(chan *task),
+	activeProj:  make(map[int]*task),
+	activeNodes: make(map[string]*task),
+	running:     0,
 }
 
+type resourceLock struct {
+	lock   bool
+	holder *task
+}
+
+var resourceLocker = make(chan *resourceLock)
+
 func (p *taskPool) run() {
-	ticker := time.NewTicker(10 * time.Second)
+	ticker := time.NewTicker(5 * time.Second)
 
 	defer func() {
+		close(resourceLocker)
 		ticker.Stop()
 	}()
 
+	// Lock or unlock resources when running a task
+	go func(locker <-chan *resourceLock) {
+		for l := range locker {
+			t := l.holder
+
+			if l.lock {
+				if p.blocks(t) {
+					panic("Trying to lock an already locked resource!")
+				}
+
+				p.activeProj[t.projectID] = t
+
+				for _, node := range t.hosts {
+					p.activeNodes[node] = t
+				}
+
+				p.running++
+				continue
+			}
+
+			if p.activeProj[t.projectID] == t {
+				delete(p.activeProj, t.projectID)
+			}
+
+			for _, node := range t.hosts {
+				delete(p.activeNodes, node)
+			}
+
+			p.running--
+		}
+	}(resourceLocker)
+
 	for {
 		select {
 		case task := <-p.register:
 			fmt.Println(task)
-			if p.running == nil {
-				go task.run()
-				continue
-			}
-
+			go task.prepareRun()
 			p.queue = append(p.queue, task)
 		case <-ticker.C:
-			if len(p.queue) == 0 || p.running != nil {
+			if len(p.queue) == 0 {
+				continue
+			} else if t := p.queue[0]; t.task.Status != "error" && (!t.prepared || p.blocks(t)) {
+				p.queue = append(p.queue[1:], t)
 				continue
 			}
 
-			fmt.Println("Running a task.")
-			go pool.queue[0].run()
+			if t := pool.queue[0]; t.task.Status != "error" {
+				fmt.Println("Running a task.")
+				resourceLocker <- &resourceLock{lock: true, holder: t}
+				go t.run()
+			}
 			pool.queue = pool.queue[1:]
 		}
 	}
 }
 
+func (p *taskPool) blocks(t *task) bool {
+	if p.running >= util.Config.MaxParallelTasks {
+		return true
+	}
+
+	switch util.Config.ConcurrencyMode {
+	case "project":
+		return p.activeProj[t.projectID] != nil
+	case "node":
+		for _, node := range t.hosts {
+			if p.activeNodes[node] != nil {
+				return true
+			}
+		}
+
+		return false
+	default:
+		return p.running > 0
+	}
+}
+
 func StartRunner() {
 	pool.run()
 }
diff --git a/api/tasks/runner.go b/api/tasks/runner.go
index d5a3f462..b6b409d3 100644
--- a/api/tasks/runner.go
+++ b/api/tasks/runner.go
@@ -8,6 +8,7 @@ import (
 	"io/ioutil"
 	"os"
 	"os/exec"
+	"regexp"
 	"strconv"
 	"strings"
 	"time"
@@ -26,6 +27,8 @@ type task struct {
 	users       []int
 	projectID   int
 	alert       bool
+	hosts       []string
+	prepared    bool
 	alert_chat  string
 }
 
@@ -36,12 +39,80 @@ func (t *task) fail() {
 	t.sendTelegramAlert()
 }
 
-func (t *task) run() {
-	pool.running = t
+func (t *task) prepareRun() {
+	t.prepared = false
 
+	defer func() {
+		fmt.Println("Stopped preparing task")
+
+		objType := "task"
+		desc := "Task ID " + strconv.Itoa(t.task.ID) + " (" + t.template.Alias + ")" + " finished - " + strings.ToUpper(t.task.Status)
+		if err := (db.Event{
+			ProjectID:   &t.projectID,
+			ObjectType:  &objType,
+			ObjectID:    &t.task.ID,
+			Description: &desc,
+		}.Insert()); err != nil {
+			t.log("Fatal error inserting an event")
+			panic(err)
+		}
+	}()
+
+	t.log("Preparing: " + strconv.Itoa(t.task.ID))
+
+	if err := t.populateDetails(); err != nil {
+		t.log("Error: " + err.Error())
+		t.fail()
+		return
+	}
+
+	objType := "task"
+	desc := "Task ID " + strconv.Itoa(t.task.ID) + " (" + t.template.Alias + ")" + " is preparing"
+	if err := (db.Event{
+		ProjectID:   &t.projectID,
+		ObjectType:  &objType,
+		ObjectID:    &t.task.ID,
+		Description: &desc,
+	}.Insert()); err != nil {
+		t.log("Fatal error inserting an event")
+		panic(err)
+	}
+
+	t.log("Prepare task with template: " + t.template.Alias + "\n")
+
+	if err := t.installKey(t.repository.SshKey); err != nil {
+		t.log("Failed installing ssh key for repository access: " + err.Error())
+		t.fail()
+		return
+	}
+
+	if err := t.updateRepository(); err != nil {
+		t.log("Failed updating repository: " + err.Error())
+		t.fail()
+		return
+	}
+
+	if err := t.installInventory(); err != nil {
+		t.log("Failed to install inventory: " + err.Error())
+		t.fail()
+		return
+	}
+
+	// todo: write environment
+
+	if err := t.listPlaybookHosts(); err != nil {
+		t.log("Listing playbook hosts failed: " + err.Error())
+		t.fail()
+		return
+	}
+
+	t.prepared = true
+}
+
+func (t *task) run() {
 	defer func() {
 		fmt.Println("Stopped running tasks")
-		pool.running = nil
+		resourceLocker <- &resourceLock{lock: false, holder: t}
 
 		now := time.Now()
 		t.task.End = &now
@@ -60,14 +131,7 @@ func (t *task) run() {
 		}
 	}()
 
-	if err := t.populateDetails(); err != nil {
-		t.log("Error: " + err.Error())
-		t.fail()
-		return
-	}
-
 	{
-		fmt.Println(t.users)
 		now := time.Now()
 		t.task.Status = "running"
 		t.task.Start = &now
@@ -90,26 +154,6 @@ func (t *task) run() {
 	t.log("Started: " + strconv.Itoa(t.task.ID))
 	t.log("Run task with template: " + t.template.Alias + "\n")
 
-	if err := t.installKey(t.repository.SshKey); err != nil {
-		t.log("Failed installing ssh key for repository access: " + err.Error())
-		t.fail()
-		return
-	}
-
-	if err := t.updateRepository(); err != nil {
-		t.log("Failed updating repository: " + err.Error())
-		t.fail()
-		return
-	}
-
-	if err := t.installInventory(); err != nil {
-		t.log("Failed to install inventory: " + err.Error())
-		t.fail()
-		return
-	}
-
-	// todo: write environment
-
 	if err := t.runGalaxy(); err != nil {
 		t.log("Running galaxy failed: " + err.Error())
 		t.fail()
@@ -296,7 +340,42 @@ func (t *task) runGalaxy() error {
 	return cmd.Run()
 }
 
+func (t *task) listPlaybookHosts() error {
+	args, err := t.getPlaybookArgs()
+	if err != nil {
+		return err
+	}
+	args = append(args, "--list-hosts")
+
+	cmd := exec.Command("ansible-playbook", args...)
+	cmd.Dir = util.Config.TmpPath + "/repository_" + strconv.Itoa(t.repository.ID)
+	cmd.Env = t.envVars(util.Config.TmpPath, cmd.Dir, nil)
+
+	out, err := cmd.Output()
+	re := regexp.MustCompile("(?m)^\\s{6}(.*)$")
+	matches := re.FindAllSubmatch(out, 20)
+	hosts := make([]string, len(matches))
+	for i, _ := range matches {
+		hosts[i] = string(matches[i][1])
+	}
+	t.hosts = hosts
+	return err
+}
+
 func (t *task) runPlaybook() error {
+	args, err := t.getPlaybookArgs()
+	if err != nil {
+		return err
+	}
+	cmd := exec.Command("ansible-playbook", args...)
+	cmd.Dir = util.Config.TmpPath + "/repository_" + strconv.Itoa(t.repository.ID)
+	cmd.Env = t.envVars(util.Config.TmpPath, cmd.Dir, nil)
+
+	t.logCmd(cmd)
+	return cmd.Run()
+}
+
+func (t *task) getPlaybookArgs() ([]string, error) {
 	playbookName := t.task.Playbook
 	if len(playbookName) == 0 {
 		playbookName = t.template.Playbook
@@ -323,7 +402,7 @@ func (t *task) runPlaybook() error {
 		err := json.Unmarshal([]byte(t.environment.JSON), &js)
 		if err != nil {
 			t.log("JSON is not valid")
-			return err
+			return nil, err
 		}
 
 		args = append(args, "--extra-vars", t.environment.JSON)
@@ -334,7 +413,7 @@ func (t *task) runPlaybook() error {
 		err := json.Unmarshal([]byte(*t.template.Arguments), &extraArgs)
 		if err != nil {
 			t.log("Could not unmarshal arguments to []string")
-			return err
+			return nil, err
 		}
 	}
 
@@ -344,13 +423,7 @@ func (t *task) runPlaybook() error {
 		args = append(args, extraArgs...)
 		args = append(args, playbookName)
 	}
-
-	cmd := exec.Command("ansible-playbook", args...)
-	cmd.Dir = util.Config.TmpPath + "/repository_" + strconv.Itoa(t.repository.ID)
-	cmd.Env = t.envVars(util.Config.TmpPath, cmd.Dir, nil)
-
-	t.logCmd(cmd)
-	return cmd.Run()
+	return args, nil
 }
 
 func (t *task) envVars(home string, pwd string, gitSSHCommand *string) []string {
diff --git a/util/config.go b/util/config.go
index 35beb21f..f92fdf25 100644
--- a/util/config.go
+++ b/util/config.go
@@ -69,6 +69,10 @@ type configType struct {
 	TelegramAlert bool   `json:"telegram_alert"`
 	TelegramChat  string `json:"telegram_chat"`
 	TelegramToken string `json:"telegram_token"`
+
+	// task concurrency
+	ConcurrencyMode  string `json:"concurrency_mode"`
+	MaxParallelTasks int    `json:"max_parallel_tasks"`
 }
 
 var Config *configType
@@ -151,6 +155,10 @@ func init() {
 		Config.TmpPath = "/tmp/semaphore"
 	}
 
+	if Config.MaxParallelTasks < 1 {
+		Config.MaxParallelTasks = 10
+	}
+
 	var encryption []byte
 	encryption = nil
 
@@ -342,7 +350,6 @@ func (conf *configType) Scan() {
 		if len(conf.LdapMappings.Mail) == 0 {
 			conf.LdapMappings.Mail = "mail"
 		}
-
 	} else {
 		conf.LdapEnable = false
 	}