diff --git a/crates/domain/src/error.rs b/crates/domain/src/error.rs
index f998b31..0563f9c 100644
--- a/crates/domain/src/error.rs
+++ b/crates/domain/src/error.rs
@@ -17,4 +17,5 @@ pub enum KernelError {
     InvalidStateTransition(ThreadId),
     InvalidThread(ThreadId),
     TooManyThreads,
+    OutOfMemory,
 }
diff --git a/crates/domain/src/lib.rs b/crates/domain/src/lib.rs
index 0479ac1..20141d1 100644
--- a/crates/domain/src/lib.rs
+++ b/crates/domain/src/lib.rs
@@ -4,6 +4,7 @@ pub mod capability;
 pub mod endpoint;
 pub mod error;
 pub mod fault;
+pub mod memory;
 pub mod message;
 pub mod process;
 pub mod resource;
diff --git a/crates/domain/src/memory/mod.rs b/crates/domain/src/memory/mod.rs
new file mode 100644
index 0000000..2b1f366
--- /dev/null
+++ b/crates/domain/src/memory/mod.rs
@@ -0,0 +1,95 @@
+use types::{
+    address::PhysicalAddress,
+    bounded::PageCount,
+    generation::Generation,
+    id::{ProcessId, RegionId},
+};
+
+pub mod page_pool;
+pub mod process_memory;
+
+#[cfg(test)]
+#[path = "tests.rs"]
+mod tests;
+
+const MAX_REGIONS: usize = 256;
+
+pub struct MemoryRegion {
+    id: RegionId,
+    owner: ProcessId,
+    base: PhysicalAddress,
+    size: PageCount,
+    generation: Generation,
+}
+
+impl MemoryRegion {
+    pub fn new(
+        id: RegionId,
+        owner: ProcessId,
+        base: PhysicalAddress,
+        size: PageCount,
+        generation: Generation,
+    ) -> Self {
+        Self {
+            id,
+            owner,
+            base,
+            size,
+            generation,
+        }
+    }
+
+    pub fn id(&self) -> RegionId {
+        self.id
+    }
+
+    pub fn owner(&self) -> ProcessId {
+        self.owner
+    }
+
+    pub fn base(&self) -> PhysicalAddress {
+        self.base
+    }
+
+    pub fn size(&self) -> PageCount {
+        self.size
+    }
+
+    pub fn generation(&self) -> &Generation {
+        &self.generation
+    }
+}
+
+pub struct RegionTable {
+    regions: [Option<MemoryRegion>; MAX_REGIONS],
+}
+
+impl RegionTable {
+    pub fn new() -> Self {
+        Self {
+            regions: [const { None }; MAX_REGIONS],
+        }
+    }
+
+    pub fn insert(&mut self, region: MemoryRegion) -> Option<RegionId> {
+        let idx = self.regions.iter().position(|s| s.is_none())?;
+        let id = RegionId::from_raw(idx as u16);
+        self.regions[idx] = Some(region);
+        Some(id)
+    }
+
+    pub fn get(&self, id: RegionId) -> Option<&MemoryRegion> {
+        self.regions.get(id.raw() as usize).and_then(|s| s.as_ref())
+    }
+
+    pub fn remove(&mut self, id: RegionId) -> Option<MemoryRegion> {
+        self.regions.get_mut(id.raw() as usize).and_then(|s| s.take())
+    }
+
+    pub fn regions_for_process(&self, process: ProcessId) -> impl Iterator<Item = &MemoryRegion> {
+        self.regions
+            .iter()
+            .filter_map(|s| s.as_ref())
+            .filter(move |r| r.owner() == process)
+    }
+}
diff --git a/crates/domain/src/memory/page_pool.rs b/crates/domain/src/memory/page_pool.rs
new file mode 100644
index 0000000..23c077a
--- /dev/null
+++ b/crates/domain/src/memory/page_pool.rs
@@ -0,0 +1,68 @@
+use types::address::PhysicalAddress;
+
+const MAX_PAGES: usize = 16384;
+
+pub struct PagePool {
+    pages: [bool; MAX_PAGES],
+    base: PhysicalAddress,
+    total: usize,
+    free_count: usize,
+}
+
+impl PagePool {
+    pub fn new(base: PhysicalAddress, total_pages: usize) -> Self {
+        let mut pages = [false; MAX_PAGES];
+        for i in 0..total_pages {
+            pages[i] = true;
+        }
+        Self {
+            pages,
+            base,
+            total: total_pages,
+            free_count: total_pages,
+        }
+    }
+
+    pub fn allocate(&mut self, count: usize) -> Option<PhysicalAddress> {
+        let start = self.find_contiguous(count)?;
+        for i in start..start + count {
+            self.pages[i] = false;
+        }
+        self.free_count -= count;
+        Some(self.base.offset(start))
+    }
+
+    pub fn free(&mut self, addr: PhysicalAddress, count: usize) -> bool {
+        if addr.raw() < self.base.raw() {
+            return false;
+        }
+        let start = (addr.raw() - self.base.raw()) / 4096;
+        if start + count > self.total {
+            return false;
+        }
+        for i in start..start + count {
+            self.pages[i] = true;
+        }
+        self.free_count += count;
+        true
+    }
+
+    pub fn free_count(&self) -> usize {
+        self.free_count
+    }
+
+    fn find_contiguous(&self, count: usize) -> Option<usize> {
+        let mut run = 0;
+        for i in 0..self.total {
+            if self.pages[i] {
+                run += 1;
+                if run == count {
+                    return Some(i + 1 - count);
+                }
+            } else {
+                run = 0;
+            }
+        }
+        None
+    }
+}
diff --git a/crates/domain/src/memory/process_memory.rs b/crates/domain/src/memory/process_memory.rs
new file mode 100644
index 0000000..d8eff63
--- /dev/null
+++ b/crates/domain/src/memory/process_memory.rs
@@ -0,0 +1,47 @@
+use types::id::ProcessId;
+
+use crate::error::KernelError;
+
+pub struct ProcessMemory {
+    process: ProcessId,
+    page_count: usize,
+    limit: usize,
+}
+
+impl ProcessMemory {
+    pub fn new(process: ProcessId, limit: usize) -> Self {
+        Self {
+            process,
+            page_count: 0,
+            limit,
+        }
+    }
+
+    pub fn process(&self) -> ProcessId {
+        self.process
+    }
+
+    pub fn page_count(&self) -> usize {
+        self.page_count
+    }
+
+    pub fn limit(&self) -> usize {
+        self.limit
+    }
+
+    pub fn grant(&mut self, count: usize) -> Result<(), KernelError> {
+        if self.page_count + count > self.limit {
+            return Err(KernelError::OutOfMemory);
+        }
+        self.page_count += count;
+        Ok(())
+    }
+
+    pub fn release(&mut self, count: usize) -> Result<(), KernelError> {
+        if count > self.page_count {
+            return Err(KernelError::OutOfMemory);
+        }
+        self.page_count -= count;
+        Ok(())
+    }
+}
diff --git a/crates/domain/src/memory/tests.rs b/crates/domain/src/memory/tests.rs
new file mode 100644
index 0000000..106c452
--- /dev/null
+++ b/crates/domain/src/memory/tests.rs
@@ -0,0 +1,207 @@
+use super::page_pool::PagePool;
+use super::process_memory::ProcessMemory;
+use super::*;
+use types::address::PhysicalAddress;
+use types::bounded::PageCount;
+use types::generation::Generation;
+use types::id::{ProcessId, RegionId};
+
+fn base() -> PhysicalAddress {
+    PhysicalAddress::from_raw(0x8000_0000)
+}
+
+fn process(id: u16) -> ProcessId {
+    ProcessId::from_raw(id)
+}
+
+fn pages(n: u16) -> PageCount {
+    PageCount::new(n).unwrap()
+}
+
+// --- PagePool tests ---
+
+#[test]
+fn new_pool_has_all_pages_free() {
+    let pool = PagePool::new(base(), 100);
+    assert_eq!(pool.free_count(), 100);
+}
+
+#[test]
+fn allocate_reduces_free_count() {
+    let mut pool = PagePool::new(base(), 100);
+    pool.allocate(10).unwrap();
+    assert_eq!(pool.free_count(), 90);
+}
+
+#[test]
+fn allocate_returns_base_aligned_address() {
+    let mut pool = PagePool::new(base(), 100);
+    let addr = pool.allocate(1).unwrap();
+    assert_eq!(addr, base());
+}
+
+#[test]
+fn allocate_sequential_returns_contiguous() {
+    let mut pool = PagePool::new(base(), 100);
+    let a = pool.allocate(4).unwrap();
+    let b = pool.allocate(4).unwrap();
+    assert_eq!(a, base());
+    assert_eq!(b, base().offset(4));
+}
+
+#[test]
+fn allocate_too_many_returns_none() {
+    let mut pool = PagePool::new(base(), 10);
+    assert!(pool.allocate(11).is_none());
+}
+
+#[test]
+fn free_then_reallocate() {
+    let mut pool = PagePool::new(base(), 10);
+    let addr = pool.allocate(5).unwrap();
+    assert_eq!(pool.free_count(), 5);
+    assert!(pool.free(addr, 5));
+    assert_eq!(pool.free_count(), 10);
+    let addr2 = pool.allocate(5).unwrap();
+    assert_eq!(addr2, base());
+}
+
+#[test]
+fn free_out_of_range_returns_false() {
+    let mut pool = PagePool::new(base(), 10);
+    assert!(!pool.free(PhysicalAddress::from_raw(0), 1));
+}
+
+#[test]
+fn allocate_fragmented_finds_gap() {
+    let mut pool = PagePool::new(base(), 10);
+    let a = pool.allocate(3).unwrap();
+    let _b = pool.allocate(3).unwrap();
+    let _c = pool.allocate(3).unwrap();
+    pool.free(a, 3);
+    // now pages 0-2 are free, 3-8 allocated, 9 free
+    // asking for 3 contiguous should find 0-2
+    let d = pool.allocate(3).unwrap();
+    assert_eq!(d, base());
+}
+
+#[test]
+fn allocate_exact_remaining() {
+    let mut pool = PagePool::new(base(), 5);
+    let addr = pool.allocate(5).unwrap();
+    assert_eq!(addr, base());
+    assert_eq!(pool.free_count(), 0);
+    assert!(pool.allocate(1).is_none());
+}
+
+// --- ProcessMemory tests ---
+
+#[test]
+fn new_process_memory_has_zero_pages() {
+    let pm = ProcessMemory::new(process(0), 100);
+    assert_eq!(pm.page_count(), 0);
+    assert_eq!(pm.limit(), 100);
+}
+
+#[test]
+fn grant_pages_within_limit() {
+    let mut pm = ProcessMemory::new(process(0), 100);
+    assert!(pm.grant(10).is_ok());
+    assert_eq!(pm.page_count(), 10);
+}
+
+#[test]
+fn grant_pages_exceeding_limit_fails() {
+    let mut pm = ProcessMemory::new(process(0), 10);
+    assert!(pm.grant(11).is_err());
+    assert_eq!(pm.page_count(), 0);
+}
+
+#[test]
+fn release_pages_reduces_count() {
+    let mut pm = ProcessMemory::new(process(0), 100);
+    pm.grant(20).unwrap();
+    assert!(pm.release(5).is_ok());
+    assert_eq!(pm.page_count(), 15);
+}
+
+#[test]
+fn release_more_than_owned_fails() {
+    let mut pm = ProcessMemory::new(process(0), 100);
+    pm.grant(5).unwrap();
+    assert!(pm.release(10).is_err());
+    assert_eq!(pm.page_count(), 5);
+}
+
+#[test]
+fn grant_up_to_exact_limit() {
+    let mut pm = ProcessMemory::new(process(0), 10);
+    pm.grant(10).unwrap();
+    assert!(pm.grant(1).is_err());
+}
+
+// --- MemoryRegion tests ---
+
+#[test]
+fn memory_region_construction_and_accessors() {
+    let region = MemoryRegion::new(
+        RegionId::from_raw(1),
+        process(0),
+        base(),
+        pages(4),
+        Generation::initial(),
+    );
+    assert_eq!(region.id(), RegionId::from_raw(1));
+    assert_eq!(region.owner(), process(0));
+    assert_eq!(region.base(), base());
+    assert_eq!(region.size(), pages(4));
+    assert_eq!(region.generation(), &Generation::initial());
+}
+
+// --- RegionTable tests ---
+
+#[test]
+fn region_table_insert_and_get() {
+    let mut table = RegionTable::new();
+    let id = table.insert(MemoryRegion::new(
+        RegionId::from_raw(0),
+        process(0),
+        base(),
+        pages(4),
+        Generation::initial(),
+    ));
+    assert!(id.is_some());
+    let rid = id.unwrap();
+    assert!(table.get(rid).is_some());
+}
+
+#[test]
+fn region_table_remove() {
+    let mut table = RegionTable::new();
+    let id = table.insert(MemoryRegion::new(
+        RegionId::from_raw(0),
+        process(0),
+        base(),
+        pages(4),
+        Generation::initial(),
+    )).unwrap();
+    let removed = table.remove(id);
+    assert!(removed.is_some());
+    assert!(table.get(id).is_none());
+}
+
+#[test]
+fn region_table_regions_for_process() {
+    let mut table = RegionTable::new();
+    table.insert(MemoryRegion::new(
+        RegionId::from_raw(0), process(0), base(), pages(4), Generation::initial(),
+    ));
+    table.insert(MemoryRegion::new(
+        RegionId::from_raw(1), process(1), base(), pages(4), Generation::initial(),
+    ));
+    table.insert(MemoryRegion::new(
+        RegionId::from_raw(2), process(0), base(), pages(2), Generation::initial(),
+    ));
+    assert_eq!(table.regions_for_process(process(0)).count(), 2);
+    assert_eq!(table.regions_for_process(process(1)).count(), 1);
+}
diff --git a/crates/domain/src/resource.rs b/crates/domain/src/resource.rs
index e825544..394c5df 100644
--- a/crates/domain/src/resource.rs
+++ b/crates/domain/src/resource.rs
@@ -1,9 +1,4 @@
-use types::{
-    address::VirtualAddress,
-    bounded::PageCount,
-    generation::Generation,
-    id::{EndpointId, IrqId, ProcessId, RegionId},
-};
+use types::id::{EndpointId, IrqId, ProcessId, RegionId};
 
 #[derive(Clone)]
 pub enum Resource {
@@ -13,10 +8,3 @@ pub enum Resource {
     Interrupt(IrqId),
     ProcessCreate,
 }
-
-pub struct MemoryRegion {
-    id: RegionId,
-    base: VirtualAddress,
-    size: PageCount,
-    generation: Generation,
-}
diff --git a/crates/types/src/address.rs b/crates/types/src/address.rs
index 4cf9197..5ef3868 100644
--- a/crates/types/src/address.rs
+++ b/crates/types/src/address.rs
@@ -7,6 +7,23 @@ pub struct StackPointer(usize);
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct VirtualAddress(usize);
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+pub struct PhysicalAddress(usize);
+
+impl PhysicalAddress {
+    pub fn from_raw(addr: usize) -> Self {
+        Self(addr)
+    }
+
+    pub fn raw(&self) -> usize {
+        self.0
+    }
+
+    pub fn offset(&self, pages: usize) -> Self {
+        Self(self.0 + pages * 4096)
+    }
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct DataRef {
     addr: VirtualAddress,